There exists an impressive quantity of literature dealing with knowledge Representation that covers highly technical contributions as well as more philosophical ones or again those that have a more or less explicit "cognitive" orientation. So, it is not very astonishing to notice that the definition of what knowledge representation is, is quite vague. It is not our intention to give a historical survey of that notion nor to proceed to a critical enumeration of the several topics that are covered by it. Our objective is, rather, to develop a conceptual framework that should permit us to handle the major descriptive problems in the conception of knowledge based systems. In order to be able to put forth in a systematic way our conception of knowledge representation (KR), we will discuss in the first section some central problems of knowledge description. In the second section, we will introduce the conceptual graph theory developed mainly by Sowa (1984) and try to give a more formal account of KR.