When organizations want to gain benefits from Enterprise Systems, em-ployees not only need to use the technology, they need to use it effectively. However, very few studies have examined what it takes for employees to effectively use new IT. In this paper, we draw on the idea of knowing-in-practice and a recent conceptualization of effective use to propose and test a new model. Our findings suggest that our concepts of social an ambidextrous knowing can well explain the emergence of effective use af-ter an ES implementation. These findings give important insights on how employees embed learning of a new ES in their daily work practices to achieve effective use. This research can contribute to a better under-standing of how actual benefits from ES can be created. Nurturing capa-bilities for knowing and supporting employees’ in their work practices seems to be more important than competency-based training.