EPA Methods 26 and 26A and Proposed Methods 0050 and 0051 are in widespread use for collection and quantitation of stationary source emissions of halogens and halogen acids from a variety of source types. Considerable research has been conducted in evaluation of these methods, but research information about the methods has not been published in one convenient summary and much of the technical community is unaware of its existence. This paper provides historical and scientific background for the EPA sampling methods in use today, along with some of their strengths and limitations. The primary evaluation studies are summarized, and publication references are given.