This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book provides the unique benefits and challenges that arise out of longitudinal sociolinguistic studies of individuals, with the explicit goal of informing future studies. It also provides a platform for panel researchers to share their experiences with longitudinal data sets. The book discusses the creation of the first ever sociolinguistic panel corpus, which grew out of the Montreal French project and which has been used for dozens of research projects on intraspeaker and community wide change. It explores the advantages and disadvantages of existing longitudinal recordings from independent sources, including cross-discipline reuse of recordings as well as raw "found" data. The book describes a collaboration with researchers in child development that facilitated their access to—and eventual expansion of—a rich source of longitudinal linguistic data: The Frank Porter Graham corpus.