International security is a term which refers to the measures taken by states and international organizations, such as the United Nations, European Union, and others, to ensure mutual survival and safety. These measures include military action and diplomatic agreements such as treaties and conventions. International and national security are invariably linked. International security is national security or state security in the global arena.

By the end of World War II, a new subject of academic study, security studies, focusing on international security emerged. It began as an independent field of study, but was absorbed as a sub-field of international relations. Since it took hold in the 1950s, the study of international security has been at the heart of international relations. It covers areas such as security studies, strategic studies, peace studies, and other areas.

The meaning of "security" is often treated as a common sense term that can be understood by "unacknowledged consensus". The content of international security has expanded over the years. Today it covers a variety of interconnected issues in the world that affect survival. It ranges from the traditional or conventional modes of military power, the causes and consequences of war between states, economic strength, to ethnic, religious and ideological conflicts, trade and economic conflicts, energy supplies, science and technology, food, as well as threats to human security and the stability of states from environmental degradation, infectious diseases, climate change and the activities of non-state actors.

While the wide perspective of international security regards everything as a security matter, the traditional approach focuses mainly or exclusively on military concerns.

Edward Kolodziej has compared international security to a Tower of Babel and Roland Paris (2004) views it as "in the eye of the beholder". Security has been widely applied to "justify suspending civil liberties, making war, and massively reallocating resources during the last fifty years".

Walter Lippmann (1944) views security as the capability of a country to protect its core values, both in terms that a state need not sacrifice core values in avoiding war and can maintain them by winning war. David Baldwin (1997) argues that pursuing security sometimes requires sacrificing other values, including marginal values and prime values. Richard Ullman (1983) has suggested that a decrease in vulnerability is security.

Arnold Wolfers (1952) argues that "security" is generally a normative term. It is applied by nations "in order to be either expedient—a rational means toward an accepted end—or moral, the best or least evil course of action". In the same way that people are different in sensing and identifying danger and threats, Wolfers argues that different nations also have different expectations of security. Not only is there a difference between forbearance of threats, but different nations also face different levels of threats because of their unique geographical, economic, ecological, and political environment.

Barry Buzan (2000) views the study of international security as more than a study of threats, but also a study of which threats that can be tolerated and which require immediate action. He sees the concept of security as not either power or peace, but something in between.