In the last decade of the last century, constructivism asserted itself as a theory of International Relations. The inability of the so-called mainstream theories to explain change, something that became particularly evident with the end of the Cold War, opened up space for a theory that conceives of reality as being socially constructed and that favours the understanding of political phenomena over their prediction. Using a qualitative methodological approach anchored in interpretivism, this article seeks to understand the relevance of the concepts of identity and ontological security in explaining change. After listing the foundational assumptions of constructivism as a theory of International Relations, such as the mutual constitution between agents and structures, the different currents are discussed, namely the conventional and the critical, thus emphasizing the pluralism of this theory. This pluralism is also evident in the different approaches to the dynamic between ontological security and identity, which is crucial to confirming the promise that constructivism brought at the end of the 20th century, i.e. explaining change. This dynamic reaffirms the understanding that the explanation of change represents an asset of constructivism as a theory of International Relations, and has contributed significantly to its affirmation.