Terms such as age, ageing, and older adults are central to the body of research explored in this book. This chapter offers an interdisciplinary overview of these concepts and examines how they are framed within older-adult HCI research. Its aim is to lay the groundwork for the discussions on older adults and digital technologies that follow in the subsequent chapters of this book. Additionally, it aims to serve as an accessible entry point for HCI scholars interested in the study of ageing, older adults, and digital technologies. To achieve this, the chapter draws on research contributions from the last twenty years or so.