ERP systems (Enterprise Resource Planning) have an enormous potential to promote the improvement of the competitive position of companies. Successful implementation of an ERP system can afford to cut operating costs, have tighter demand forecasts, speed production cycles and improve customer service (Umble et al. 2003).However, the results obtained with its implementation aren't often so positive. Studies like the Langenwaltre (2000) indicate that between 40 and 60 % of implementation projects of ERP systems can be classified as failures.Although these data can be questioned, if we regard that too often companies have dealt with these projects without fully assess what should be its rate of return (Umble et al. 2003) or that IT investments involve for business improvements that hardly can be assessed by ROI (Peerstone Research 2004). On the other hand, it also highlights that the positive results in implementing ERP systems doesn't occur automatically but they need to be given certain circumstances linked mainly by the implementation process itself.The participation of the authors of this paper in the implementation of ERP's and methodologies of process improvement, has allowed to set some of the key factors to consider in carrying out this process of integration successfully.