In this paper the authors attempt to explain and sharpen unresolved issues and questions that have evolved in the study of careers, especially since the concept of "careers" has received increased theoretical and empirical attention across disciplines. The issues discussed involve (1) conceptualization and measurement of careers; (2) dimensions of jobs and careers; (3) structural and person-level predictors of career phenomena; and (4) life course dimensions and the age-time specificity of relationships. Building on earlier research by Seymour Spilerman, the authors introduce their conceptualization and measurement of career lines. (Career lines are described as empirically linked sequences of jobs formed by institutional and labor market structure.) They discuss the theoretical methodological, and data requirements for further informing the understanding of career development. (Author/BM)