Informatics and Internet in particular favor largely the collection of data without user permission, their disclosure to third parties and their cross-analysis. The density of the human activities in the digital world thus constitutes a fertile ground for potential invasions of privacy of the users. Our works examine first the legal context of privacy protection, as well as the diverse computing means intended for the protection of personal data. A need for user centered solutions emerges, giving him/her more control over his/her personal data. In this perspective, we analyze European and French privacy legislation to extract data protection axis. Then we specify the constraints related to these axes, and we introduce them in existing security policy models. Thus we suggest the application of one model for both access control and privacy protection. The access control model should be extended by new privacy related conditions and parameters. To do so, we define the language XPACML (eXtensible Privacy aware Access Control Markup Language) based on XACML and new privacy extensions. Placed in an E-commerce context, we define a semantic model allowing to represent various electronic transactions contexts, and leading to a dynamic generation of context- aware XPACML policies. Looking for a vast protection of the personal data, we dedicate the last part of our works to the possible negotiations which can be made between a user and a service provider. Two protocols are proposed. The first one permits the negotiation of the terms and the conditions of data protection policies, while the second permits the negotiation of the requested data themselves
