One of the emerging trends in advanced human-computer interaction is the increasing portability of computing devices. Some experts predict that wearable computers are the next generation of portable machines. Worn on the body they provide constant access to computing and communications resources. The objective of wearable computer design is to merge the user's information space with his or her workspace. The wearable computer should offer seamless integration of information processing tools with the existing work environment. To accomplish this, the wearable system must offer functionality in a natural and unobtrusive manner, allowing the user to dedicate all of his or her attention to the task at hand with no distraction provided by the system itself. In this survey paper, definition, main components and characteristics of wearable PCs are introduced. A survey of the academic and research institutes leading research projects in wearable PCs is presented. These on-going projects are generally falling into four research areas, namely, local communications, eyeglass displays, speech interaction and mobile applications. In this overview paper, the wireless link methods and wireless communication features in the area of local communication are emphasized, progress to meet the technical challenges in eyeglass display is reported; and on-going research in the area of speech interaction is briefly described.