Pablos Heredero, Carmen de2010-02-042010-02-042009978-1-60566-892-5http://hdl.handle.net/10115/3062The implementation of an Enterprise Resource Planning System (ERP) is a risky and high cost action, even more when we are dealing with small and medium sized enterprises. Although many studies have shown the importance of paying attention to critical success factors in ERP implementations, there is still a high degree of failures and bad experiences around ERP implementations. Most literature review has shown experiences of success and failure coming from big sized firms. But there is a lack of information of what has happened in the area of small and medium size firms, and for some economies, they are essential. In this book chapter we try to show a model containing the main elements that can better explain the degree of success and of failure in ERP implementations by providing examples mainly affecting to the circumstances of small and medium size firms. In our model we propose 5 main groups of variables affecting final results in ERP implementations, Key words, ERP system, critical success factors, change of processes, managerial support, processes.enEmpresainfo:eu-repo/semantics/book10.4018/978-1-60566-892-5.ch026info:eu-repo/semantics/openAccess5311 Organización y Dirección de Empresas