Based on the organizational learning perspective, we present an empirical model to explain the assimilation of complex enterprise systems. We conceptualize systems implementation capability of organizations in terms of two types of knowledge – artifactual knowledge and inter-unit coordination knowledge. We propose that these knowledge dimensions are directly related to the degree of assimilation of enterprise systems. Further, considering that assimilation of IT innovations is steeped in the institutional environment, we also consider the moderating effects of mimetic and normative institutional pressures on the relationship between implementation knowledge and the degree of assimilation. Analysis of survey responses from ERP implementations in seventy-seven organizations reveals support for our main hypotheses that both the implementation knowledge dimensions directly affect assimilation. We also confirm that while mimetic institutional pressures positively moderate the impact of ERP-specific artifactual knowledge on assimilation, normative influences positively moderate the effect of ERP-specific coordination knowledge on assimilation. However, surprisingly mimetic pressures negatively moderate the impact of ERP-specific coordination knowledge on assimilation. The negative moderation suggests that organizations with greater interunit coordination knowledge are more ‘mindful’ towards ERP assimilation and therefore mimetic pressures play a lesser role in affecting assimilation levels. Our findings offer interesting implications for theory and practice.