Abstract
<jats:title>Abstract</jats:title> <jats:p>This chapter aims to provide guidance on how to conceptualize “intensive” longitudinal studies that capture participants’ daily lives at multiple times over (relatively) short intervals. Such methods are especially valuable for research questions concerning the emergence, change, and stability of specific phenomena, such as identity within individuals over time. This is relevant in emerging adulthood, which sees fast changes with often important life-long outcomes. The chapter outlines key decisions that researchers must make when designing such studies, including the formulation of a research question; the choice of a timescale; operationalization of the intensive measure of the phenomenon under study; choosing an assessment method and the choice for a qualitative, quantitative, or mixed methods design; choosing a sample size; and selecting participants and building a relationship. Rather than advocating for a particular methodology, the chapter provides examples of studies and a detailed case study to illustrate these decisions.</jats:p>