Social media technology has enabled virtual collaborative environments where people actively interact, share knowledge, coordinate activities, solve problems, co-create value, and innovate. Organizations have begun to leverage approaches and technologies to involve numerous people from outside their boundaries to perform organizational tasks. Despite the success and popularity of this 'crowdsourcing' phenomenon, there appears to be a distinct gap in the literature regarding the empirical evaluation of the factors involved in a crowdsourcing user experience. This paper aims to fill this void by proposing a theoretical model of the antecedents and their relationships for crowdsourcing user engagement. It is defined as the quality of effort online users devote to collaboration activities that contribute directly to desired outcomes. Drawing from research in psychology and IS, we identify three critical elements that precede crowdsourcing user engagement: personal interest in topic, goal clarity, and motivation to contribute. This paper examines the theoretical basis of these variables of interest in detail, derives a causal model of their interrelationships, and identifies future plans for model testing.