Cardiac CT scanners are rapidly improving, each major vendor has introduced a state of the art scanner every 2–3 years. The basic applications, terminology and acquisition has not changed dramatically, however, improvements in hardware and software continue to reduce radiation exposure, scan times, artifacts and improve image quality. This chapter outlines the basic CT terminology, functions and background behind the current state of CT scan- ners for cardiac applications. It reviews spatial, temporal and contrast resolution limits of the CT scanners. An overview of common terms, radiation exposure and protocols are included. This acts as an introductory chapter to be expanded by subsequent chapters that will each go into more details on specific topics. Comparison to magnetic resonance for image quality and functionality, and dose comparisons to mammography, nuclear and fluoroscopy are included.