This paper provides an overview of eye tracking, a multidisciplinary research field that monitors eye movements to determine gaze point or motion patterns. Eye tracking has many applications, such as face detection, usability testing, biometric identification, human behavior studies and human-computer interaction. The paper focuses on remote eye tracking, which does not require physical contact with the user, and discusses the state-of-the-art work in this field. The paper also presents the hardware components and computer vision processes involved in remote eye tracking systems, and shows how they can be developed with low-cost off-the-shelf hardware.