Images of the gods were omnipresent in the Roman world. Cult images served many functions, but some were the focal point of ritual activity in temples and are termed ‘idols’ in this book. After exploring both the ancient and modern terminology of cult images, this chapter turns to evidence for belief in the divinity of idols. Many ancient writers, including Arnobius of Sicca, give a sense that many Romans perceived idols to be divine, or at least endowed with agency. It is suggested that this aspect of Roman religion can be understood through cross-cultural comparisons and anthropological theories of agency in religious art. To help us build a complete picture of the place of Roman cult images in Roman religion, and to avoid the problem of the so-called museum effect, the book adopts a biographical approach, exploring the births, lives, and death of cult images. It focuses on cult images and temples in the western Roman Empire, including Rome, Gaul, and Germany, from the Roman Republican period, or the pre-Roman Celtic and Germanic Iron Age, to late antiquity and the early medieval period.