Since 1970 Islamist political parties have participated in at least 76 parliamentary elections in 17 Muslim-majority countries. This paper first identifies an empirical pattern in Islamists’ electoral performance over time and then draws lessons from the history of European electoral socialism to predict the effect of electoral participation on the movement for Islamism. The paper also compares two Islamist movements that attempted to broaden their support beyond their initial base. Despite participating in parliamentary elections under a wide variety of electoral systems and political and social contexts, I find that Islamists’ vote shares exhibit a remarkably similar trend over time. With a few notable exceptions (e.g. Palestine, Iraq), Islamists’ vote shares tend to increase from election to election until stabilizing around 11-20%. In countries with the most parliamentary elections since 1970, such as Malaysia, Indonesia, and Bangladesh, Islamist vote shares oscillate around this stable level. The pattern of Islamists’ electoral performance resembles European socialists’ votes which increased over time until stabilizing between 30-50%. European socialists initially participated in elections for reasons remarkably similar to Islamists; both socialists and Islamists saw elections as offering a ‘peaceful revolution’ that would reform unjust societies and provide conditions for universal liberation. They sought (or seek) a mandate for legislating society, respectively, into socialism or Islamism. Fitting with this year’s theme of change, ‘old’ European electoral socialism has lessons for today’s electoral Islamism. I argue that Islamists, like electoral socialists before them, are finding that they must choose between a party homogenous in its Islamist appeal but sentenced to perpetual electoral minorities or a party that appeals to other voters but at the cost of diluting its Islamist orientation. I examine the one Islamist movement that significantly expanded its vote share beyond this 11-20% barrier. After a decade of electoral failures, Turkish Islamists grew their vote share rapidly from 15% in 1999 to 34% in 2002 to 44% in 2007 after Islamists split and the AK Parti credibly recast electoral Islamism as a center-right movement. I also examine the Jordanian Islamist Movement to understand how it has attempted to reformulate its message to appeal beyond its limited Islamist base. European socialist parties serve as shadow cases.