This article reviews the current state of the literature on the assessment of bipolar disorder in adults. Research on reliable and valid measures for bipolar disorder has unfortunately lagged behind assessment research for other disorders, such as major depression. We review diagnostic tools, self-report measures to facilitate screening for bipolar diagnoses, and symptom severity measures. We briefly review other assessment domains, including measures designed to facilitate self-monitoring of symptoms. We highlight particular gaps in the field, including an absence of research on the reliable diagnosis of bipolar II and milder forms of disorder, a lack of empirical data on the best ways to integrate data from multiple domains, and a shortage of measures targeting a broader set of illness-related constructs relevant to bipolar disorder.