The share of voters participating in national elections from abroad is evergrowing. Despite this, expatriates constitute one of the most understudied groups of electors. Some existing analyses have shown that expatriates support different parties than voters residing at home. However, the reasons for this effect remain in the dark. In this article, we test common electoral theories—socio-structural, socio-psychological, and issue voting—and their relevance for voters at home and abroad. Additionally, we test if differences in voting behaviour are due to compositional or behavioural reasons. In line with previous studies, we show that expatriates support other parties, in the Swiss case left parties, than voters at home. We further show that this gap cannot be explained by the different composition of the expatriate community but rather by their different behavioural motivations. Expatriates more often base their vote choice on their social class and religious beliefs. Partisanship voting and, to some extent, issue voting are less important in the expatriate community. The findings are based on the Swiss National Election Study 2011 and additional interviews conducted among Swiss residing abroad.