Organisations have invested in self-service information systems (IS) to provide a direct interface for service delivery. Enriching the usage of these systems can provide organisations with immense benefits. However, limited research has been directed towards understanding post-adoption IS usage behaviour in general and specifically in the context of self-service IS. This study proposes post-adoption IS usage behaviour as a broader concept constituting feature level usage of IS, integration of IS in the work system and exploration of new uses of IS. We evaluate how the new conceptualisation can be used to classify users at different stages of self-service IS usage. Further, we examine user perceptions that differentiate among the users situated at different selfservice IS usage stages. Data were collected in the context of a self-service Web-based IS to validate the post-adoption IS usage constructs and to examine the proposed thesis. The newly developed conceptual structure and measures for post-adoption IS usage behaviour exhibit strong psychometric properties. The analysis shows three distinct post-adoption IS usage stages and highlights that usefulness, user-initiated learning, ease of use, satisfaction and voluntariness of use differentiate users at the different stages of post-adoption IS usage. The results show that these variables aggregate into value confirmation and learning orientation as two higher-level concepts. Further, we evaluate the predictive efficacy of the research model in classifying users into different post-adoption self-service IS usage stages. Implications are drawn for future research.

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This article builds upon the technology acceptance model and theories of technology sensemaking to explore pre-enterprise system adoption expectations and post-enterprise system adoption outcomes in a longitudinal setting. Building on the exploitation and exploration paradigm, we propose that task productivity and task innovation expectations are the key drivers of users' pre-adoption enterprise system usage intention. Further, we argue that the enterprise system facilitates generation of a common knowledge base that may encourage a more integrated organizational culture and promote shared understanding among employees. Considering the distinction between mandatory and voluntary contexts, we propose that user acceptance of the enterprise system at the pre-and post-adoption stages will mediate these relationships in a mandatory context. The results show that the influence of pre-adoption expectations regarding task productivity and task innovation on intention to use an enterprise system is mediated by user acceptance of the enterprise system. Intention to use an enterprise system is positively related to actual use. At the post-adoption stage, the influence of actual use on shared understanding is mediated by user acceptance of an enterprise system and enterprise system use has a direct negative impact on task efficiency in the initial period after implementation. Overall, the results highlight that user acceptance at both pre-and † Corresponding author. 660Understanding Enterprise System Use and Impact post-adoption stages are critical factors when usage is mandatory. These findings suggest a number of important implications for research and for managerial action.