The French Socialist Party has maintained a deeply ambivalent relationship with political radicalism. Throughout its long history, political radicalism has been experienced both as an internal political contest (hence as a form of intra-party struggle for influence) and as a relationship within (and beyond) the broader party system. This article identifies three levels of analysis as heuristics to facilitate a study of the French Socialist Party over the long term. From the perspective of the party as a whole, the party evolves according to its own eco-system, and is shaped by deeply embedded cultural and political traits. A different level of analysis frames the question of political radicalism organizationally, in terms of relations within and beyond the party. Finally, one can also understand the party's relationship with political radicalism instrumentally and strategically, in terms of electoral alliances. Though there is a tension between these three approaches, each contributes to understanding why the French Socialist Party is sometimes considered a European exception.