Health Technology Assessment (HTA) is a process that uses principles from across various disciplines, including medicine, sociology, economics, and ethics, to evaluate health technologies. Policy makers can use HTA as a tool to assess health technologies in a systematic, unbiased, transparent, and robust manner in order to make informed and evidence-based decisions. Generally, researchers begin an HTA by defining the overall scope of the assessment, after which they choose an appropriate type of health economic evaluation, one of the most important elements of HTA. The objective of this article is to provide recommendations about the scope of HTA as well as guidance on the kinds of health economic evaluation that are appropriate in the context of the new Thai HTA guidelines. A well-defined research question that addresses five major components-target population, technology or intervention, comparator outcome of interest, and perspective-is an essential