The concept of personal control is examined as this relates to the conceptual design of personal ventilation systems based upon the body's physiological and psychological homeostatic requirements. Literature on the effects of personal control of environmental conditions is reviewed. The concept of a "just noticeable difference in discomfort" that underpins the desire to initiate some personal control action is discussed. The concept of personal control is symmetrical for thermal conditions (hot or cold) but, apart from some pleasant fragrances, is asymmetric for indoor air quality (where less pollution is better). Factors that may influence the exercise of personal control will be summarized. Finally, important information for the design of PVS systems that are both energy efficient and effective in optimizing the micro-environmental conditions for workplace employees will be presented.