The proliferation of pervasive information systems’ research has motivated a gradual technological shift away from the desktop computing paradigm towards more ubiquitous forms of information systems presence and use. This progression towards pervasive IS is accompanied by an implication that there exist clear and unambiguous boundaries between pervasive and non-pervasive information systems. This study poses that this implied dichotomy is not an accurate reflection of reality and proposes a more accurate conceptualization of pervasiveness through developing its construct. In particular, it adopts the methodological approach of construct development and reports the results from two of the three phases, i.e. definition of construct’s domain and instrument development. A preliminary instrument was developed through literature analysis and then was assessed for its content validity through a survey of experts (N=33). Experts recognized ubiquity and context awareness as the two determinant characteristics of pervasiveness while diffusion was perceived as the ultimate goal of a pervasive IS and not as a technology characteristic. The final pervasiveness instrument can be exploited by information systems researchers aiming to enrich their own theoretical propositions by taking into account how pervasiveness influences things like technology acceptance and usability evaluation.