In this research we describe the institutionalization process of an organizational field: that of ERP customization choices. We will ground our analysis on the case of a public sector organization in the course of 10 years. Implementation choices evolved according to a process where pressures towards cross-unit homogeneization were followed by a period of internal differentiation. A subsequent time period of inter-organizational and inter-regional homogeneization gave rise to a time period of particularization based on local organizational contexts. The processual analysis of implementation choices let us conclude that the evolution of the organizational field of customization choices can be described as a framing/overflowing dynamics where actors and relations and the ‘situation’ in which the issue of similarity can be addressed vary according to a discountinuous and recursive pattern and that actors consciously use space and time as resources in their search for niches of autonomy.