Wearable technology, as a new application environment for electronic and computing devices of all kinds, presents many new challenges to designers. The fields of human-computer interaction and functional wearability must each address new problems in the design of wearable technology. Wearable technology also introduces new social concerns, as it can mediate the ways in which an individual is perceived by others, interacts with others, and manages his/her own physical space. Because the field of wearable technology is very new, the design of wearable technology is still relatively unexplored. The dominant design culture in current wearable technology research, that of electrical engineering and computer science, is unused to addressing variables related to the human body, mind, and social interaction. Good design choices for wearable technology depend on understanding and acknowledging the wide array of interdisciplinary variables that affect user interaction with a wearable device. The functional apparel design culture brings an interdisciplinary approach to wearable technology design, and its structured design process offers designers a means of organizing and addressing issues, and identifying new variables to be considered in future work. This thesis seeks to use the functional apparel design process to approach the new variables involved in the interface between the body-mounted device and the human user in three areas: an input device (a bio-monitoring bra), an output device (a shoulder pad vibrotactile display), and the aesthetic and psychological issues of visual representation of technology (a set of massage shirts). These projects address physical, cognitive, and social user needs in wearable technology. The development of the shoulder pad vibrotactile display sought to create an intuitive, visually subtle, physically comfortable tactile display device within a standard garment insert, using the volume of the shoulder pad as an integration space. The evaluation process found the use of a pre-existing garment space such as the shoulder pad to be successful for the integration of electronics, and the device to be perceptible at a low level of resolution. The bio-monitoring bra study evaluated several variables involved in the use of garment-integrated contact (not adhesive) electrodes for bio-monitoring, an input modality that creates a low cognitive load for the user. Garment-integrated electrodes were designed to replace the medical standard adhesive electrodes, to increase the physical and social comfort of the user. Contact electrodes were tested in both an EMG (muscle activity) configuration and in an ECG (heartbeat) configuration. The ECG configuration recorded a useable signal during periods of low activity level, but the EMG configuration was not able to capture useful muscle activity data. A set of massage shirts was developed to investigate the varying social needs of users regarding the visual display of garment functionality. Two focus groups were conducted, and an application was chosen (shoulder and back massage) that was attractive and useful to subjects with a wide variety of personality types and aesthetic tastes. Three prototypes were constructed, with the same vibrating shoulder and back massage, but with the embedded technology concealed or displayed to varying degrees. These prototypes were evaluated, to determine the relationship between subject self-perceived personality and desire to conceal or display technology. Results showed the application to be attractive to most users, and aesthetic needs to be quite varied, even within an individual. The functional apparel design process, as well as the knowledge and intuition about the body interface gained from the study of functional apparel design can help to broaden the scope of interdisciplinary variables considered in the design of wearable technology, and thereby produce a more successful design.