[en] This document is the 2005 activity report of the French atomic energy commission (CEA). The CEA is a main actor of nuclear research, development and innovation and is involved in three main domains: energy, defense/security, and information/health technologies thanks to high quality research works. With a manpower of 15000 researchers and collaborators with internationally acknowledged competences, the CEA is a driving force of industrial innovation and develops partnerships with French and European industries. It also warrants the perenniality of nuclear dissuasion. This report presents these different aspects of the CEA activities: 1 - defense-security: simulation program, opening to the scientific community, nuclear warheads, nuclear propulsion, cleansing of Rhone valley facilities, permanent monitoring of treaties respect, fight against terrorism; 2 - energy: optimization of the industrial park, advances in long lived radioactive wastes management, future nuclear systems, cleansing and dismantling integration, European nuclear energy research, new energy technologies; 3 - information and health technologies: major challenge of micro- and nano-technologies, key role of software technologies and complex systems; 4 - big research facilities opened to the scientific and industrial communities; 5 - scientific status: scientific evaluation process, prices and honors; 6 - programs support: revisited strategic control, confirmed simplification, active employment and training policy, teaching and training, technological valorization, international relations, communication, continuous quality approach, mastery of facilities safety, security, environmental control, a key-year for information systems. A financial report is attached to the document. (J.S.)