This article addresses the overlooked subject of party switching in the Canadian House of Commons for the period 1945–2011. We estimate a model that explores how and why MPs engage in the otherwise risky behaviour of abandoning their party labels in a system characterized by a low personal vote. Our findings suggest that the electoral consequences for MPs who switch parties for policy reasons are indistinguishable from MPs who do not switch at all. By contrast, MPs who switch parties for office-related reasons, such as to accept a seat in cabinet or vote-related reasons, experience large electoral penalties. We also find that MPs who are expelled from caucus face the strongest electoral penalties of all party switchers, indicating it matters whether an MP jumps or is pushed. Our findings suggest that voters recognize opportunistic behaviour among their legislators and punish them accordingly and that under some circumstances, party switching may be both strategic and rational.