Tax compliance nudges -- behavioral interventions that aim to increase tax compliance without changing the underlying economic incentives of taxpayers -- are used increasingly by governments because of their potential cost-effectiveness in raising tax revenue. In this project we collect about a thousand treatment effect estimates from 45 randomized controlled trials, and use methods of meta-analysis to give systematic answers to questions like: i) Are nudges effective in curbing tax evasion? ii) If so, on which margins of compliance and by how much on average? iii) Which nudge types work more effectively? iv) Are nudges effective also in the longer horizon? v) Which groups of taxpayers are more responsive to nudges? vi) Do nudges work in specific settings (e.g., low compliance environment) or more generally? In answering these questions, we aim to present a systematic review of the literature and to provide guidance for further tax experiments and policy interventions.