The selection and measurement of competencies, reflecting educational effects in a lifelong learning perspective, represents a major challenge for the German National Educational Panel Study (NEPS). Data on the development of competencies serves as a central point of reference for all other parts of the study. These competencies have to be relevant not only for a successful and responsible individual life but also for a well-functioning modern democratic society. Hence, the aim is not just to describe the development of such competencies, but also to analyze relevant prerequisites, conditions, and courses of competence acquisition. The lifelong learning perspective will shed light on how different competencies are acquired over the life span, how they interact over time and across educational stages, and in which way they may contribute to individual and group-specific life-course outcomes. This chapter gives an overview on the selection, rationale, and conceptualization of competencies within NEPS.