This chapter identifies assessment instruments commonly used to assess anxiety and depression in psychosocial oncology research and summarizes the evidence regarding the relative merits of these instruments. Over the past decade, there has been considerable research examining how well brief assessment instruments function as screening tools for detecting clinically significant problems in emotional well-being. Given these developments, this chapter also identifies brief assessment instruments that can be used to screen for anxiety and depression and summarizes available evidence regarding how well they function if used for this purpose. Several conclusions are drawn: (1) two widely used instruments are most consistently rated positive; (2) no single instrument can be recommended for all possible applications; (3) existing reviews of assessment and screening instruments are characterized by a number of features that limit their utility; and (4) clinicians and researchers need to stay abreast of ongoing research likely to influence future recommendations.