Copenhagen School (international relations)
The Copenhagen School of security studies is a school of academic thought with its origins in international relations theorist Barry Buzan's book People, States and Fear: The National Security Problem in International Relations, first published in 1983.  Theorists associated with the school include Barry Buzan, Ole Wæver and Jaap de Wilde. Many of the school's members worked at the Copenhagen Peace Research Institute. 
The concept of 'sectors' concerns the different arenas where we speak of security. The list of sectors is primarily an analytical tool created to spot different dynamics. In Security: A New Framework for Analysis, the authors list the following sectors: military/state, political, societal, economic and environmental. As such, CS theory can be regarded as 'widening' traditional materialist security studies by looking at security in these 'new' sectors.
The concept of regional security complexes covers how security is clustered in geographically shaped regions. Security concerns do not travel well over distances and threats are therefore most likely to occur in the region. The security of each actor in a region interacts with the security of the other actors. There is often intense security interdependence within a region, but not between regions, which is what defines a region and what makes regional security an interesting area of study. Insulator states sometimes isolate regions, such as Afghanistan's location between the Middle East and South Asia. Insulators mark boundaries of indifference, where security dynamics stand back to back. They contrast with the traditional idea of 'buffer states' which are located at points where security dynamics are intense (e.g. Belgium between Germany and France). 
Regional Security Complex Theory should not be confused with Regionalism, a subset of IR from the 1970s concerned mostly with regional integration. For more on regional security, see Buzan's Regions and Powers.[full citation needed]
citation needed], and the one that has generated the most literature. It is argued that 'security' is a speech act with distinct consequences in the context over international politics.[by whom?] By talking security an actor tries to move a topic away from politics and into an area of security concerns thereby legitimating extraordinary means against the socially constructed threat.  Instead securitization of a subject depends on an audience accepting the securitization speech act.[
Some of the most detailed books on the subject are:
- Understanding Global Security, Peter Hough,Routledge, 2004
- Barry Buzan, People, States and Fear, ECPR, 2007
- The Empire of Security, William Bain, Routledge, 2006
A criticism that has been advanced against the Copenhagen School is that it is a eurocentric approach to security.  Realists have also argued that the Copenhagen School's widening of the security agenda risks giving the discipline of security studies "intellectual incoherence". Lene Hansen has criticized the absence of gender in the Copenhagen School's approach. Other critiques focus on the role of the security analyst and the potentially conservative nature of the theory.
- Welsh School (Security Studies)
- Paris School (Security Studies)
- Critical Security Studies
- Third World Security School
- McSweeney, Bill (1996). "Identity and Security: Buzan and the Copenhagen School". Review of International Studies. doi:10.1017/S0260210500118467.
- Buzan, Barry; Wæver, Ole; de Wilde, Jaap (1998). Security: A New Framework for Analysis. Boulder, Colo.: Lynne Rienner Pub. ISBN 978-1-55587-603-6.
- Mutimer, D. (2007) Critical Security Studies: A Schismatic History in Contemporary Security Studies, A. Collins (eds.), Oxford:Oxford University Press, p. 60
- Buzan, Barry; Wæver, Ole (2003). Regions and Powers: The Structure of International Security. Cambridge University Press. p. 41. ISBN 978-0-521-89111-0.
- Wilkinson, Claire (March 2007). "The Copenhagen School on Tour in Kyrgyzstan: Is Securitization Theory Useable Outside Europe?". Security Dialogue 38 (1): 5–25. doi:10.1177/0967010607075964.
- Hansen, Lene (June 2000). "The Little Mermaid's Silent Security Dilemma and the Absence of Gender in the Copenhagen School" (PDF). Journal of International Studies 29 (2): 285–306. doi:10.1177/03058298000290020501.
- See Huysmans, ‘Revisiting Copenhagen’; Johan Eriksson, ‘Observers or Advocates?: On the Political Role of Security Analysts’, Cooperation and Conflict 34, no. 3 (1999): 311-3; and Giovanni Arcudi, ‘La Sécurité Entre Permanence et Changement’, Relations Internationales, no. 125 (2006): 97-109
- Barry Buzan, Ole Wæver & Jaap de Wilde (1998), Security: A New Framework for Analysis, Lynne Rienne
- Bill McSweeney, ‘Identity and security: Buzan and the Copenhagen school’, Review of International Studies, 22:1 (1996) 81-93.