This paper investigates the link between IT and firm performance by combining different theoretical perspectives and emphasizing the role of routines in IT-Business alignment. The basic concept of routines is operationalized and presented in an algebraic form allowing for explicit modeling and using of findings from the literature on the resource based view (RBV) and IT-Business alignment. How to use IT to gain a sustainable competitive advantage and in turn a plus in firm performance is a key question in IS research. This paper contributes to this discussion by combining different theoretical perspectives and making them explicit. The results show that indeed routines are a fundamental concept to understand the linkage between IT resources and firm performance. The proposed model shows the functional relations known from literature that have not been explicated so far.