What is soft power, and how can we analyse it empirically? The article proposes a social constructivist take on soft power by anchoring it to the concept of collective identity, and by suggesting a set of criteria that can be used to assess whether soft power is present in a relationship between two or more states. It argues that soft power is generated through continuous renegotiation of collective identity. We can assess the weight of a state’s soft power vis-a-vis another state by investigating the extent to which the discursively constructed collective identity projected by the first state is accepted or rejected by different audiences in the second state, and by examining the ability of these audiences to affect the process of foreign policy decision-making. To illustrate this approach, the article applies it to an analysis of Russia’s relationship with Ukraine prior to the 2014 crisis. In the late 2000s–early 2010s, Russia’s dominant identity was increasingly associated with the idea of a ‘Russian world’ — an imagined community based on the markers of the Russian language, the Russian culture and the common glorious past. Despite a significant increase in Moscow’s public diplomacy activities in Ukraine around that time, those efforts did not and could not fundamentally transform the psychological milieu in Moscow’s relationship with Kyiv because the projected identity was inherently incompatible with one of the main identity discourses in Ukraine and was only partially compatible with another.