This monograph is an edited collection of chapters within the domain of developmental methodology that collectively share the following goals. First, this monograph provides updated and comprehensive, yet also accessible and brief, summaries of our current understanding of key methodologies used in developmental science. Second, this monograph describes how our current understanding can be further leveraged to advance understanding of human development. Third, this monograph identifies shortcomings in our understanding of developmental methodology in order to provide a roadmap for future methodological advances. Fourth, this monograph aims to organize developmental methodology as a subdiscipline within developmental science. The chapters of this monograph were selected to identify major themes of developmental methodology, broadly defined to encompass issues of design, analysis, and research progression. Besides covering a wide range of topics, chapters were selected that (a) represent active areas of research or debate, (b) are important in advancing the quality of developmental science, and (c) seem likely to remain active and important areas of developmental methodology in the foreseeable future. Early chapters focus on design issues, including the merits of different sampling strategies and the use of large-scale data sets in developmental science. In the middle chapters, attention shifts to issues in longitudinal design and analysis. These chapters include an overview of longitudinal analyses in developmental science, considerations in measurement within longitudinal studies, and person-specific longitudinal approaches. Later chapters consider broader issues of replication and research accumulation, as well as the history and future of developmental methodology.