After decades of marginalization, there has been a swift—meteoric, even—rise in governments recognizing the need to mainstream gender perspectives across efforts to fight terrorism. Here we ask: how this happened, what it all means, and what animates the gender dimensions of counterterrorism (CT) and preventing or countering violent extremism (PVE, CVE) policies as they manifest at the United Nations and in the organizational priorities of regional and specialized entities (e.g., NATO, European Union), as well as at the national level. In a second article, we will identify what is problematic in this uptake of gender mainstreaming and diagnose why these problems are emerging, before proposing some fixes.