Debates about Slovenian interest for NATO membership should take into account basic characteristics of international security conditions after Cold war. In this period efforts for maintaining security are linked to enlargement of West-European institutions, while traditional security concepts, like achieving balance of power with alliances or neutrality are less relevant. Beside its characteristics of defense alliance, NATO also possess characteristics of security institution and successfully adapts its agenda to new circumstances in which states are not faced primarily by military threats,but with more complex security problems. NATO is institution, which provides dialog, co-operation and enhances transparency. For that reason, in conditions after the Cold war that are characterized by uncertainty, membership in NATO is an objective of numerous transitional countries. The most voiced problem linked to Slovenian candidacy for NATO lies in meeting conditions in military-defense area, partly due to the fact that reforms, planned in the past were only partially realized. Continuation of these reforms will be necessary, not only because of interest for NATO membership, but also because of the narrowing gap between political-economic and military-defense compatibility of Slovenia with Western-European states. From that reasons the costs of military-defense reforms could not be linked exclusively to NATO membership. Additionally, NATO membership does not affect only military-defense posture of the state. With NATO membership, Slovenia could not escape future security problems. Evidently the present members also face such problems, but Slovenia could enhance institutional possibilities foraddressing problems of security.