Insecure work has become increasingly frequent in recent decades. It includes insecure employment contracts (contractual arrangements that deviate from permanent, open-ended contracts) as well as perceived job insecurity (an individual perception that one’s job is at risk). While research on insecure work (contractual and perceived) has identified numerous work-related and health-related outcomes, a limited number of studies have investigated if union membership may be a protective factor. The unionization rate among workers with insecure employment contracts is relatively low, despite these contractual arrangements often being characterized by poor working conditions. This chapter reviews previous research to address the following questions: (1) How do insecure workers view union membership and what are their unionization behaviours (joining and leaving)? (2) Can union membership and support buffer the negative effects of insecure work on work-related and health-related outcomes? (3) How can unions represent the interests of insecure workers?