Cognitive Warfare is now at work in modern conflicts. This article aims to give a definition by distinguishing cognitive warfare from the simple field of psychological operations, have a part concerns the CW, and operations in the fields of information and cyber, other parts of which also concern the CW. The large majority of the CW is in no way reducible to any of these areas. The CW relies on the dimensions of information processing by the human brain to bring out representations, decisions and programming of the action, for individuals and for groups, and which are all targets of the CW.