In this chapter, we provide a summary of the association between depression and the onset of theperimenopausal transition. We begin by summarizing the timing and classification criteria traditionally used to describe the perimenopausal transition. A discussion then follows regarding theaccepted diagnostic criteria for determining new and recurrent onset of mood disorder, and difficultissues surrounding its measurement. We continue with a critical review of the literature on the association between depression and the perimenopausal transition, with particular attention being paidto issues of age at the time of the transition, the temporal relation between depression and themenopausal transition, and covariates that can influence the association. We conclude with a discussion of the importance of understanding the association and the need for further research to clarifythe risks and benefits of hormone replacement therapy.