To control is to bring two elements together and identify the differences. Control is a natural act that man has always performed. It is an organizational act inherent to any organized group. This common act will become, in the best organized companies, an activity specific to professionals who will focus on assets and accounts in order to detect possible misappropriations and recording errors. The effectiveness of internal control is conditioned by the respect of a certain number of principles. In order to achieve the objectives mentioned above (protection and safeguarding of assets, quality of information), internal control relies on a set of formalized procedures, methods and controls implemented by the administrative organization. Through this book, we have tried to highlight the importance of the evaluation of internal control in an audit mission in terms of orienting the audit program towards areas of risk and lightening the work of auditing the accounts. After having proceeded to the examination and the evaluation of the procedures constituting the cycle Purchasing-suppliers.