Augmented Reality (AR) is a new technology that involves the overlay of computer graphics on the real world. It is a live view of a physical, real world whose elements are augmented by computer generated sensory input i.e. sound, video, graphics or GPS data. AR is within a more general context termed Mixed Reality (MR) that refers to a multi-axis range of areas that covers Virtual Reality (VR), AR, telepresence, and other related technologies. This paper presents an overview of basic concepts of AR and its aspects. It briefs about the main fields in which AR is applied these days and important AR devices. Characteristics and future directions will also be discussed on this paper.