In this first chapter, we introduce The Routledge International Handbook of Constructivist Grounded Theory in Educational Research. Following an introduction and overview, in Section 1.2, we trace the history and development of Grounded Theory (GT) through a brief examination of Glaser and Strauss’s seminal work, their subsequent divergence, the development of Charmaz’s Constructivist Grounded Theory (CGT) school, and Clarke’s Situational Analysis. Next, we examine core GT principles and features and discuss each with a particular focus on how they differ in the context of the various ‘schools’ or variants of GT. Section 1.4 briefly explores recent developments, texts, and concerns in GT and CGT. Finally, we end the chapter by previewing the contents of the five parts of the Handbook.