This is more of an exploratory post where I try to share some of my thoughts and experience working in international tax. I'm also happy to answer questions (to the extent I can) if people want clarifications or more details about any of this. 

Thanks in particular to David Nash for his encouragement and help in reviewing my drafts.

Summary

• International tax rules govern how taxing rights are allocated between countries. 
• International tax policy is likely to be an impactful cause area: 
  • Not only is there a significant amount of tax revenue at stake, there is a broader indirect impact as international tax rules can constrain domestic tax policies. 
  • International tax rules tend to be relatively sticky, persisting for decades.
  • In recent years, as international tax has gotten increasingly political, there may also be broader foreign policy implications.
• Yet international tax seems to be relatively neglected. 
  • Domestic tax issues tend to be more politicised, possibly because they affect voters more directly. 
  • International tax can be highly technical and rather opaque. 
• Tractability depends on how you identify the “problem”:
  • In my view, a problem is that the development of international tax policy is dominated by relatively wealthy countries (particularly the US), who focus too heavily on their own national interest. 
  • While I doubt this broad problem can ever be fully “solved”, I believe individuals can still play a significant role in mitigating it. 

Problem 

International tax policy plays a key role in determining how much companies are taxed and where. This in turn affects the level of tax revenue different countries get. 

The development of international tax policy is dominated by the Organisation for Economic Co-operation and Development (OECD), which is made up of relatively wealthy countries. The US also plays a key role in international tax policy.^[1] I believe that many people currently working in international tax policy focus too heavily on their national interest over the global interest. 

The problems here are not ones I think we can hope to fully "solve", as the problems stem from the underlying power dynamics between developed and developing countries and the natural incentives for government officials to prioritize their own country. 

However, international tax policy could still be a worthwhile area to consider working in, because it seems to be a relatively neglected space where individuals can have a surprisingly large impact in mitigating these problems. 

Background 

What is international tax policy?

In broad terms, international tax policy governs how taxing rights are allocated between countries as well as matters of tax administration such as information sharing and dispute resolution. 

Countries enter into bilateral tax treaties that aim to prevent double taxation (i.e. when two or more countries try to tax the same income) without creating opportunities for tax avoidance or evasion. 

In recent years, there has also been a focus on multilateral tax projects, which may or may not result in a formal tax treaty. 

Bilateral DTAs 

A bilateral double tax agreement (DTA) is a tax treaty entered into by two countries. 

When a person/entity resident in one country earns income from another country, both countries may attempt to tax the same income. Such double taxation would inhibit cross-border investment and trade, so countries enter into bilateral DTAs to prevent this. Depending on the circumstances, DTAs will allocate taxing rights over the income to either:

• the residence country — where the person/entity earning the income lives or is managed; or 
• the source country — where the income is earned. 

In very broad terms, in a treaty negotiation, developed countries generally want to increase the residence country's taxing rights, because they tend to have wealthy residents that invest abroad and earn foreign income. Developing countries tend to want to increase the source country's taxing rights, so that they can tax income earned by foreign investors. 

Virtually all bilateral DTAs are based on the OECD Model Tax Convention. There is also a UN Model Tax Convention, which is very similar to the OECD Model but with stronger taxing rights for source countries. 

The OECD Model and its accompanying Commentary are updated every few years or so. The changes are discussed and negotiated by the OECD's  "working parties", which are made up of delegates from each of the OECD member countries. The delegates are tax experts (i.e. they come from a country's Treasury or tax department, not from its foreign affairs department). 

Multilateral projects 

Work on multilateral tax projects is also largely led by the OECD. In 2016, a much larger group called the Inclusive Framework was formed to undertake some of this multilateral work. Over 140 countries and jurisdictions are currently part of the Inclusive Framework. However, there is debate over how "inclusive" this arrangement truly is. The OECD still takes a leading role (because it is where the tax expertise and resources are). Recently, developing countries have been pushing for the UN to have a bigger role. 

Multilateral tax projects can result in a multilateral treaty (e.g. the Convention on Mutual Administrative Assistance in Tax Matters facilitates the exchange of information between tax authorities in different countries, including through the Automatic Exchange of Information (AEOI)).

However, as noted above, multilateral projects may not necessarily result in a treaty. For example:

• The Base Erosion and Profit-Shifting (BEPS) project which began in 2012 resulted in a list of measures which countries were either required or encouraged to adopt. Although there was a multilateral treaty to help countries to update their existing DTAs to incorporate the measures, countries did not have to sign it and were free to update their DTAs via bilateral agreements instead. 
• A global minimum tax, known as Pillar Two of the Two-Pillar Solution resulted in a set of Model Rules, which countries are expected to incorporate into their domestic laws. The rules are designed so that even if some countries don't implement the Model Rules, the minimum tax should still be effective.

ITN analysis

Disclaimers: 

• This is just based on my individual experience working on international tax policy in one OECD country. It would be great to get input from others who also have experience in this space.
• While I have attended a few OECD and Inclusive Framework meetings in which these issues have been debated, I have not worked at the OECD myself. As such, I do not really understand the inner workings of the OECD.
• Many key Inclusive Framework decisions are made at the Steering Group level. I have not attended any of these meetings.

Impact

The impact of working in international tax seems high, for the following reasons:

• The amount of tax revenue at stake is quite high 
• International tax constrains domestic tax policies
• International tax reforms are relatively “sticky” (i.e. slow to change)
• International tax disagreements could spill over into broader foreign policy 

Amount of tax revenue at stake is quite high

Estimating the amount of tax revenue affected by international tax rules is difficult. Treaties have both a direct and indirect impact and the direct impact, being the amount of tax actually relieved by a treaty, is likely to be relatively small. The indirect impact, being the cross-border investment and trade that otherwise would not take place, or that is shifted as a result of the treaty, is likely to be much greater.

Corporate income tax revenues are more likely to be impacted by international tax rules than other bases such as personal income taxes or consumption taxes (however, see my next point about international tax constraining domestic policies). One estimate of the annual amount of global corporate income tax (CIT) revenue is around US$2.4 trillion,^[2] roughly 15% of total tax revenues. 

International tax constrains domestic tax policies

Before I actually worked in tax policy, I did not appreciate how international tax can constrain domestic tax policy. 

It does this in at least three ways:

• Tax competition. For example, many countries look to international norms when setting corporate tax rates because capital tends to be mobile and they want to attract (or at least not discourage) investment. The corporate tax rate a country chooses can then also constrain personal tax rates, because if individuals can pay less tax by diverting income through companies, they will do so. While countries may have measures that try to counteract this, those measures will usually not be 100% effective and tend to be costly to enforce. 
• Tax treaties. As explained above, countries enter into DTAs, which often contain clauses that limit how each country may tax the other country’s residents and citizens. For example, DTAs usually limit the withholding tax rates a source country may impose on dividends, interest and royalties, and the countries will also be limited to the definitions of “dividends”, “interest” and “royalties” used in these DTAs. So even if they change their domestic law to increase withholding taxes on interest or broaden the definition of “royalties”, an existing DTA may override it. (The domestic law change would still have effect to the extent where there is no DTA, though.) 
• Arbitrage opportunities. Inconsistent tax systems give rise to international arbitrage and avoidance opportunities. For example, a common argument against wealth taxes and death duties is that they are too easy to avoid if the taxpayer moves to another country. Arbitrage opportunities can also prevent some innovative tax systems from being tried. For instance, a country that shifts its tax base from income to consumption by allowing a full deduction for investment/savings might find its tax base obliterated if taxpayers can too easily record “investment” there without increasing their real investment in the country. While I don’t want to suggest that the risk of creating arbitrage opportunities is insurmountable, it can be a formidable challenge. 

A possible exception to this is the US, which may have enough weight/influence to effectively force other countries to change their tax systems. They are also unique in having a citizen-based tax system, which reduces concerns of tax-induced migration, at least for individuals. 

International tax reforms are relatively “sticky” 

Bilateral DTAs are pretty sticky. Many last for decades because it is a lot of effort to renegotiate them and both countries must be willing to prioritize it. 

Multilateral reforms are even more sticky because of the difficulty in getting multiple countries that may have diverging interests to agree. The current international tax framework was established in the early 20th century and many think it hasn’t changed enough to keep up with modern developments. 

A key issue with the current framework is that taxing rights are primarily based on physical presence — e.g. factories, offices, employees, etc. Many people think this is no longer appropriate given the Internet and how globalized the economy is now. A firm today can do a lot of trade with a country without having to pay income tax there if it has no/limited physical presence in that country. 

In recent years, some countries have enacted digital service taxes, which impose tax even if the firm has no physical presence in the country. These are unilateral measures, which are not covered by existing tax treaties, and which the US considers to be discriminatory. The US has therefore responded by threatening to impose tariffs on relevant countries to counteract the revenue they would get from digital service taxes.

Pillar One of the Two-Pillar Solution is intended to be a multilateral alternative to digital services taxes. If successful, it would arguably be the biggest change to the international tax framework since WWII. (However, this is a big "if" and many commentators have voiced doubts about whether Pillar One will succeed.) 

Broader foreign policy aspects

International tax seems to have gotten increasingly political in recent years, particularly as large multinationals have gotten widespread attention for not paying “enough” tax. As noted above, Pillar One is intended to be part of the solution for this — and is very political. Some believe that Pillar One is a real test for the multilateral rules-based order. If the Pillar One proposal falls over, there could be more unilateral taxes as well as tariffs and trade wars.

Another foreign policy angle is the growing tension between developing and developed countries in tax policy development. Also as noted above, some developing countries have been pushing for the UN to have a bigger role in developing international tax policy because they consider the UN to be more inclusive and have greater legitimacy than the OECD.^[3] 

Neglectedness

My view is that the neglectedness of international tax is also high. 

The areas of tax that tend to be highly politicised seem to have a domestic focus, probably because they directly affect voters and are easier to understand (e.g. what tax rates should be, whether wealth taxes are good, etc). International tax, by contrast, is highly technical and often requires understanding other countries’ tax systems. Most private sector practitioners also have limited engagement with tax treaties. 

International tax also tends to be dominated by tax experts rather than foreign diplomats. Diplomats may often be more engaged with the public and media, which could be part of the reason international tax gets relatively little attention. 

Tractability

This is the area I am least certain about as it is highly dependent on what aspect you're assessing. Overall I would assess tractability as low. 

However, even if we cannot solve the entire problem, I think individuals can have considerable impact given how high "Impact" and "Neglectedness" seem to be. Moreover, there currently seems to be more traction than there has been in a long time, given the Pillar One and Pillar Two work and the UN/OECD turf war mentioned above. 

Possible roles for individuals

OECD Secretariat

Potential Impact

I have not worked at the OECD but my impression is that Secretariat members are given a fair degree of autonomy in how to progress their workstreams. 

While countries ultimately are the ones that agree or not to proposals, I believe OECD Secretariat can be incredibly influential because:

• How proposals are framed initially makes a big difference in how they are received by countries. 
• Country delegates often have to be across many or all workstreams while each OECD Secretariat member may just work on a few. As such, OECD Secretariat will be far more familiar with the technical details in their workstream. 
• Many of the smaller, technical details will have important consequences but are not things that countries are willing to die in a ditch over, so OECD Secretariat can sometimes  put in whatever they think is sensible. This is especially the case if there is a lot of time pressure and country delegates have to pick their battles.  
• OECD Secretariat members also play a key mediation role in getting countries that start out with differing positions to agree (e.g. by surfacing concerns and suggesting alternative compromises). Some OECD people are more or less effective at this, and I think it can make a difference in whether or not an overall agreement is reached.  

Other considerations

• Must live in, or be willing to commute to, Paris. 
• My impression is these are highly competitive and quite demanding roles. 
• Good career capital.

Country delegate 

A country delegate represents their country in tax treaty negotiations and/or at OECD/Inclusive Framework meetings. 

The role usually sits in a country's tax policy function, within the Treasury or Finance department. The role may be more or less specialised depending on the country — some delegates only do international tax and treaties, while others also work on domestic tax policy. 

Potential impact

The potential impact you can have as a delegate will depend on your seniority and on your country. 

Senior delegates will have more influence through their relationships with other country delegates. Delegates can also be elected Chairs of the OECD Working Parties, where they have more influence still. 

If you are in the US you would have a much bigger impact as a country delegate as the US voice is always given considerable weight. On the flipside, I expect it would be harder to work up to an influential role within the US Treasury. (But I could be wrong — this area might be relatively neglected within the US Government too.)

If you are in an OECD country, this might be a particularly high-impact path, especially if your country does not have sizable think-tanks or international charities. While larger countries like the US hold more sway at the OECD level, smaller countries can have a big impact relative to their size since they still have a seat at the table. Sensible suggestions can also find support regardless of which country it comes from. 

Other considerations

The job will usually involve international travel, which can be a pro or a con. 

Apart from that, what the job is like and how stressful it is will depend heavily on your country and perhaps even the culture within your particular organisation or team. Some countries, especially those with just one or two delegates, rarely intervene or make submissions. Other countries are heavily involved in almost all proposals. There are also countries in between these two extremes. 

While countries that are heavily involved tend to have larger teams to spread the workload, it can still be very demanding. Some deadlines are unreasonably tight and there can also be long virtual meetings at unsociable hours (depending on your time zone). 

It was not, in my experience, all that hard to become a country delegate. Again, this will depend on your country, but the level of competition seems to be lower than for other foreign policy roles (e.g. within foreign affairs departments).  

African Tax Administration Forum (ATAF)

Many African countries have very limited tax policy resources. There is a lot of material to get across to understand the proposals and the timeframes allowed are very tight, because of the political commitments made to reach agreements by certain dates. Even my OECD country struggles with resourcing all of this work, and I can only imagine it's much harder for most of the African countries, especially if English is not their native language. 

ATAF helps African countries cope with this policy workload. I don't know the details of how ATAF works, but I do know they put in comments on multilateral proposals and speak up at meetings on behalf of their member countries. 

United Nations 

I don’t think the UN has any tax policy staff at all. If they do, it won’t be many. My understanding is they rely on a committee of tax experts instead, with those experts nominated by countries. These are not full-time jobs. Many of these experts are also country delegates, so the best path to becoming a UN tax expert is probably to become a country delegate.

Tax Inspectors Without Borders (TIWB)

TIWB is a joint OECD/UN initiative. I don't know a lot about this role, only what I've read from public materials. 

TIWB are mostly looking for experienced auditors/tax inspectors that can help developing countries build up their audit capacity. They do not seem to offer entry-level positions or full-time jobs — instead, they look for recently retired or currently serving tax officials. 

TIWB’s work is a bit different from what I’ve been describing above, as their main work (audit) is different from policy. But apparently they are looking to expand to provide support in other areas, including tax treaty negotiations and implementation. 

Personal fit

Background and skills

• Law. Helpful for reading and interpreting treaties. But interpreting treaties is a bit different from interpreting domestic laws, so a legal background is not essential (at least in my country). 
• Economics/Finance. Again, helpful but not essential. You don't need to be great with numbers but it’s good if you can work through and understand complex tax examples and understand why tax laws are designed the way they are (they often have economic underpinnings). 
• Relationship, people, communication skills. It’s helpful if you can read a room, understand other people's points of view, communicate your ideas effectively, and find ways to bridge disagreements.

Ideas for testing your fit or getting started 

• Follow OECD work — they run a video series called OECD Tax Talks (I've never watched these myself, though.)
• OECD internships
• Policy internships/jobs in your home country. 
• Tax internships/jobs at law firms or accounting firms. 

I only have experience with the last one — I did a brief stint in tax at a large commercial law firm before moving to policy and found it gave me a good grasp of tax laws, particularly those relevant to large multinational corporations. 

My law firm experience also gave me better technical tax knowledge than my colleagues who had worked the equivalent number of years in tax policy. This is because advice had short turnaround times so I worked on many pieces of advice and had to quickly familiarise myself with different areas of tax. In contrast, policy projects take a long time so you might end up working on the same project for months or even years. 

However, note that law and accounting firms will not necessarily give you transferable skills — it depends on what work you get at these firms. If you end up doing compliance work or advice for high net worth individuals, you may not get a solid grounding in international tax. 

1. ^{^}

   Some argue that the US has too much influence at the OECD because they are the single largest funder of the OECD. Others, however, argue that the US does not have enough influence, given that some of its States by themselves are larger than many OECD countries.
   
   More generally, US domestic tax reforms have often spurred international tax reforms — examples include the US's FATCA regime leading to international AEOI, and US CFC rules causing other countries to adopt similar CFC rules. 

2. ^{^}

   A recent OECD estimate says Pillar Two is expected to raise between USD 155-192 billion per year, which represents an increase of between 6.5% to 8.1% of global corporate income tax (CIT) revenues.  I've just reversed the calculation to get the CIT figure. 

3. ^{^}

   While I personally have a lot of sympathy for these concerns, the practical reality is that: (1) the OECD is much better resourced and has both the funding and the necessary tax expertise; and (2) whatever the UN comes up with will be toothless if developed countries refuse to agree to it. For example, as noted above, the UN Model Tax Convention gives greater taxing rights to source countries but developed countries are more likely to follow the OECD Model.