The term international tax law means laws that stem from domestic sources and international sources, that refer to taxation in cross border situations.
See 2.2 of International Tax Law by Peter Hongler, 2021
International tax law is found in:
1) International Tax Agreements:
As with the DTAs, these other types of international agreements are most often bilateral, but may also be multilateral (for example, there is a Convention on Mutual Administrative Assistance in Tax Matters between OECD member countries).
2) Domestic laws that consider the jurisdiction to tax entities, and that concern the taxation on foreign income of residents (worldwide income), domestic income of non-residents and cross-border transactions.
Double taxation occurs when a taxpayer is subject to comparable tax on the same income or gains in more than one country, which in effect taxes income twice.
Double Tax Agreements (DTAs) aim to prevent fiscal evasion regarding taxation, and to avoid prevent the double taxing of income by allocating taxing rights over this income between the treaty partner countries. The taxing rights may either be exclusive to one of the treaty partners, or shared between them.
DTAs are usually bilateral, but can also be multilateral treaties between several countries in a region (for example, there is a Nordic DTA) or under the auspices of a regional organisation (for example there is a DTA between the members of the Caribbean Community organisation, CARICOM).
The most common form of DTA is treaties for the avoidance of double taxation of income and capital. Measures in such treaties to prevent tax evasion typically include exchange of information provisions and other forms of mutual assistance. Another common type of DTA covers the avoidance of double taxation in respect of inheritance (or estate) and gift taxes.
See also the following open access journal articles from SSRN on double taxation, which are a good introduction to the topic: