System use has been simply defined and measured. In this research, we investigate the dynamics of system use at the individual level. A new concept called adaptive system use is developed to capture user modifications to their use of system features. A causal model including antecedents of adaptive system use is developed. Three antecedents of adaptive system use are identified. Using a sample of 282 users of MS Office, our study examines the psychometric properties of adaptive system use and confirms the research model. Four types or dimensions of adaptive system use are trying new features, feature substitution, feature combination, and feature repurposing. Triggers are found to be the most important antecedent of adaptive system use. Facilitating conditions also affect adaptive system use significantly. Research and practical implications are offered.