Social media sites (e.g., Facebook, Twitter, Voxer, Instagram, etc.) have become platforms for self-directed professional development and learning (PDL) for many educators, including physical educators and sports coaches. The aim of this chapter is to provide an introduction to this current monograph on physical educators' and sports coaches' social media use for PDL by presenting key issues and relevant literature, and previewing the chapters to follow. The chapter begins with a background discussion of social media, followed by brief literature reviews of PDL research in education and physical education and sport pedagogy, and research on social media use for PDL. Next, an overview of key theories and concepts used within the monograph is provided. The chapter concludes with individual summaries of the six empirical chapters of the monograph.