This chapter brings to the fore key issues and challenges in second language (L2) pronunciation assessment, drawing on both psycholinguistic and sociolinguistic perspectives. After providing reasons for the exclusion of pronunciation from L2 classrooms and its marginalization from mainstream L2 assessment research over the past several decades, the role of pronunciation in theoretical models of communicative competence and in L2 oral proficiency scales is examined. The theme of defining and operationalizing an appropriate assessment criterion for L2 pronunciation permeates the chapter and existing empirical evidence on the pronunciation features that should be taught and, by implication, tested is considered. The chapter concludes with future directions in L2 pronunciation assessment research, with particular emphasis on influences on rater judgments of L2 speech and technological innovations.