Strengths assessments focus on the individual's talents, abilities, resources, and strengths. No systematic review of strengths assessments for use within mental health populations has been published. The aims of this study were to describe and evaluate strengths assessments for use within mental health services. A systematic review identified 12 strengths assessments (5 quantitative, 7 qualitative). The Strengths Assessment Worksheet (SAW) was the most widely utilized and evaluated qualitative assessment. Psychometric properties of the assessments were assessed against set quality criteria. Data on psychometric properties were available for 4 measures. The Client Assessment of Strengths, Interests and Goals (CASIG) had the strongest psychometric evidence. The SAW and CASIG assessments can be tentatively recommended within clinical practice, although the evidence for all strengths assessments is currently limited. To describe the content of the strengths assessment, the items used to operationalize the concept of strengths in each assessment were extracted and themed. Twenty-four themes were identified and organized into 3 overarching categories: individual factors, environmental factors, and interpersonal factors. These categories form the basis of an empirically based definition of strengths that could be used as a conceptual foundation for new clinical assessments.