Companion diagnostics are those that are needed to identify patients for which a specific therapeutic is safe and effective. Examples of these include Her2/neu FISH and IHC assays for patients considered for Herceptin therapy. This roundtable will focus on the challenges of designing studies in which questions regarding the therapeutic and diagnostic need to be addressed. It will also focus on the importance of the analytical performance of the studies. Companion diagnostics are reviewed by both CDRH and CBER and the roundtable chair has been involved in such submissions in both centers of FDA.