Switching between social identities can help us to adapt to different contexts. Based on socio-psychological theories, we are likely to perform frequent switches, yet little is known about the effectiveness of social identity switches and how much control we have over them. Our research firstly aims to address this gap in knowledge by determining whether – and at what level of integration into the self-concept – a social identity switch impairs the activation of the next identity (“identity activation cost”). To address this question, we conducted a first set of studies (Studies 1 - 3) in which we prompted social identity switches and measured identity salience implicitly. Across different measurement methods, results indicate that participants were highly effective in switching social identities. Secondly, Studies 4 and 5 address potential differences in identity activation during switches between identities at different levels of integration into the self. We found that switches remained highly effective even when switching away from a novel (rather than well-established) social identity. An effect of cross-categorisation in Study 5 was possibly due to greater learning of individual stimuli in this study. Based on the support we found for relatively rapid and effortless social identity switches, our third aim was to investigate how much control we have over such switches. Specifically, Studies 6 and 7 focus on whether we can decide to keep a social identity salient by preventing a switch away from it when the social context would likely make another identity salient. Results indicate that we have limited control over social identity switches. Our research holds important theoretical implications by testing fundamental assumptions of self-categorisation theory, as well as practical implications for managing multiple identities in everyday life. We outline ideas for future research, including research on characteristics of different social identities as well as situational characteristics that might affect the ability to switch between identities and control switches.Engineering and Physical Sciences Research Council (EPSRC)Engineering and Physical Sciences Research Council (EPSRC)EPSRC