Researchers and practitioners have paid much attention to the impacts of information technologies (IT). However, while studied at the organizational level extensively, the impact of IT use at the individual level receives less attention. Therefore, my dissertation is aimed at a deeper understanding of the impacts of IT use on the individual work-related performance. This research involves two Phases. In Phase I, I will reconceptualize IT use. Based on a comprehensive literature review, I found that IT use is obviously a critical concept yet previous conceptualizations of IT use are not sufficient. IT use has been measured primarily by the amount of time, the frequency and duration, and tasks completed. Other aspects of IT use should also be considered. Therefore, I first apply activity theory and other relevant theories to deconstruct and reconceptualize the too simply defined IT use. According to activity theory, an activity involves three major components: subjects and objects that are mediated by tools. Their interactions are also influenced by organizational and technological environments. Activity theory provides us a new perspective to analyze IT use behavior. In Phase II, the nomological values of the new conceptualization of IT resulting from Phase I will be examined. Specifically, I will consider the relationships between IT use and its antecedents (personal traits, perceptions, etc) and consequences (performance). This research has implications for both researchers and practitioners.