Augmented reality (AR) combines real and virtual images, is interactive in real-time, and has virtual content registered in 3D space. The document traces the history of AR from early experimentation in the 1960s-1980s to mainstream commercial applications today. Key developments include the first head-mounted display in 1968, mobile phone AR in the 2000s, and consumer products like Google Glass. The document also provides examples of AR applications in various domains such as marketing, gaming, manufacturing, and healthcare.