In this article, we examine the occurrence of pre-electoral coalitions (PECs). Recent research points to when and why they are likely to occur, but these explanations are pitched at aggregate level, and they are less satisfying when applied to our particular cases. Rather than institutional or party-system features, we concentrate on the parties themselves – a level of analysis that raises theoretical and methodological challenges, which we discuss. Empirically, we investigate two cases of PEC in 2005–2006. One involved three Norwegian left-of-centre parties, the other involved four Swedish right-of-centre parties; both marked major departures from established behavioural patterns. We suggest certain conditions that may be necessary for a PEC to be formed. In particular, we argue that ‘decisive’ parties must prioritize office at the moment of decision, and that this preference order may be induced by some sort of environmental or intra-party stimulus.