This article, having mobilized multiple theoretical frameworks to understand the dynamics of a decision process concerning IT, draws up an explanatory model that it refines with the case study of three groups of Tunisian companies.

The results of this exploratory research show that the acquisition of an ERP system and its implementation represents a strategic event for the company given the cost and scope of this project. However, this decision is often made based on "confidence" and not based on the necessary feasibility and profitability studies. It is therefore non-economic rationality that explains a large part of the ERP acquisition decision-making process. This rationality includes the influence of the institutional environment with its internal and external components. In addition, the non-economic rationality incorporates the impact that the organizational culture can have.