This report aims to establish a strong evidence base for planning a validation study of professional standards for teachers. It presents findings from a rapid "snapshot" review of relevant research literature, to identify previous examples of validation studies, and extract lessons from these about worthwhile methods and considerations in research design. This review was originally conducted to inform the design of a validation study of the draft Myanmar Teacher Competency Standards Framework, but may also have wider relevance to other education systems pursuing similar standards-based reforms. This report presents findings from the literature review. It is divided into four sections: 1. What does "validity" mean? 2. How can validity be demonstrated? 3. Validity and reliability. 4. Policy considerations. The report also includes two recent detailed case studies, from Vietnam and the Philippines.