Traditionally, security policy has been an issue area characterized by formal treaties (e.g. START, NPT etc.) and highly institutionalized organizations (e.g. NATO, UN). The move from bipolarity to multipolarity and the rise of new security risks and challenges seem to require more flexible and inclusive institutional forms. The old institutional structure is persistent and still legitimate despite enormous deficits in effectiveness and efficiency. This is probably why informal forums are increasingly used to explore new modes of security governance. Informalization is the tendency of state and non-state actors to engage in collective action on the basis of flexible coalitions, bypassing traditional international institutions or compromising legal obligations by substituting them for less binding arrangements. However, informalization offers not only opportunities, but also entails risks. The opportunity is to adapt to new political circumstances, challenges and crises more promptly, and to include new emerging powers and stakeholders into the international governance structure. The risk is to sidestep more formal traditional institutions (like the UN) and to undermine established practices of international cooperation drifting toward less transparent and legitimate procedures. This round table aims at discussing the weakness of established formal institutions as well as at exploring both potential strengths and weaknesses of new informal ones.