The article reflects a topical problem for theory and practice of international relations. The intensification and expansion of the European integration building is a new and contradictory process that scientists and politicians are required to comprehend the crux of the existent. The article discusses the main theoretical approaches to the research of one of the European integration realm - security and defence policy. The analysis of the theoretical directions is taken on the basis of comparison of its approaches to interpretation of reasons of the Common Security and Defence Policy (CSDP) of the European Union (EU) emergence and development. There are three theoretical approaches to interpretation of integration process: neorealism, neofunctionalism and neoliberal intergovernmentalism. From the position of neorealism the CSDP emergence is a EU effort to change the balance of power in the new international relations system after the end of the Cold War. The CSDP is covered both classically and by a wider sense of the term "balance of power" by neorealists. Representatives of the "soft balancing" theory consider that the CSDP emergence is caused by the rivalry of west European states and the USA. There is an alternative theory of "balance of threats"; accordingly, the integration in security and defence realms is due to emergence of new power poles or sources of threats, and not to the European countries' anxiety of the USA domination. In this case the key thesis of the approach is the influence of structural changes in the international relations system. The neofunctionalists conform to the logic of the spill-over effect, according to which the emergence of defence cooperation is explained by integration expansion from economics to politics. The intensification of integration is stimulated by the system of supranational bodies, whose nature stipulates the tendency to cooperation. The activation of the CSDP development after the changes of Great Britain's position due to Labourites' coming to power in 1997 testifies to the high extent of the inner factors influence. This determinant is amplified with longstanding France's urge towards the development of the European security system, its support by Germany and ambiguous attitude to the CSDP of other EU states. The selected factors found its reflection in the theory of neoliberal intergovernmentalism, whose main ideas are aimed at the research of bottom-up policy-making mechanism and founded on the theories of liberal regimes, negotiations and intergovernmentalism. The article rightfully concludes, that the presented approaches have definite limitations hindering from a comprehensive analysis of the European integration. However, the reviewed theoretical approaches do not contradict each other, which makes it possible to combine in the analysis specific historical aspects including security and defence policy.