Responding to ongoing debates about the presence (or otherwise) of feminism within left-wing politics, this article has two central aims. First, it seeks to develop a set of analytical criteria to identify and assess the extent to which an instance of politics has become “feminist.” Second, it aims to illustrate the utility of this framework by applying it to a range of examples of contemporary left politics in Britain. Our argument is similarly twofold. Conceptually, learning from the literature on socialist feminism, gender and politics, and cultural studies and sociology, we identify five features of what we call “feministization,” arguing that in addition to feminist ideas, policies, and modes of organizing, we must also pay attention to the role of embodied performances and affect. Empirically, we suggest that, seen through this lens, the British left has in fact undergone a significant but uneven process of feministization in recent years.