The end of the XXth century and the beginning of the XXIst have been marked both by the growth of globalization’s amplitude and by the changes of the international security environment. The main threatens are terrorism, mass destruction weapons, the growing world polarisation between rich and poor, the faulty governance, the emphasize of the rivalries between the biggest economic powers of the world. Crises and conflicts management as well as the effective control of a war suppose a collective defence, namely alliances and coalitions, as no country is able to defend by itself, so far. Of course, collective defence does not exclude the national one, but the latest depends on the first. The present paper attempts to explain Romania’s role as a security beneficiary and provider in South-Eastern European security environment, as a member of both EU and NATO.