Chapter 1 is in two parts. The first section traces the history of SCEDs, including the early concepts differentiating single-case from between-groups methodology. Then follows the types of studies that were conducted in neurorehabilitation between the 1960s to 1980s and we point the reader to the Appendix, in which we summarise 66 recently published SCEDs. This is followed by a selection of surveys of SCEDs in various fields, focusing on the different types of methodological designs used. The second part of the chapter focuses on basic concepts used in SCED methodology and throughout the book. First, we define SCEDs, and then provide a conceptual framework of nine types of single-case designs commonly reported in the literature, including the medical N-of-1 trial. We then provide a set of definitions of commonly encountered terms used through the book. The chapter concludes with a rationale for the importance of graphical representation of SCED data, followed by the current standards of evidence for SCED studies.