The advancement and spread of technology have improved options for clinical assessment. Specifically, ambulatory assessment (AA) methods have improved the ability to assess constructs with a particular focus on intra-individual and dynamic time processes, which are highly relevant to the assessment of mood and behavior. This chapter reviews current technologies, including applications of online platforms and devices, often utilized to collect data in an AA framework, and discusses their applications within research and clinical settings (e.g., assessment of mood instability). AA has a number of benefits, including limited or no reliance on retrospective recall as well as the ability to assess context and construct of interest in the “real world,” and allows for the ability to gather rich information regarding mood, behavior, and psychophysiology as part of the clinical assessment process. Much of the clinical application of AA is in the early stages. A number of important considerations and recommendations, including data security, accessibility, and future directions, are also reviewed within the context of AA methods.