We have developed a maturity model of the source-to-pay process (S2P, from sourcing planning to payment), a tool that allows us to represent, analyze and improve the complete supply management in small and medium size companies, public and privates. Pacma Model provides an integrated framework of business processes, management indicators, best practices and new technologies, improving efficiency and achieving cost reductions in Purchasing and related activities. Implementing the model imply establishing a new business perspective, in which the Purchasing area evolves from a support function towards an agent of change and strategic partner within the company, leading the change towards comprehensive management of the supply chain.