Tax authorities in key Asian jurisdictions have introduced thin capitalization regimes that provide for an arm's length analysis. As such, it is important and useful for tax and finance executives to know how to conduct and document such an analysis. This article provides practical guidance to conducting an arm's length analysis on thin capitalization and sets out best practices on preparing and maintaining supporting documentation. Topics considered include possible means by which the tax authorities may apply the arm’s length principle in the context of working a thin capitalization case, and a discussion of those things that tax authorities tend to like and dislike seeing in reviewing a taxpayer's documentation.