Niche parties often originate in social movements, yet the latter's role in shaping these parties has received scant attention. I argue that movement roots can help niche parties achieve both vote-and policy-seeking goals by keeping core issues salient, bolstering issue ownership and securing allies in civil society. Employing interviews with movement, as well as Green and Pirate party leaders in Sweden and Germany, I identify three mechanisms (electoral pressure, grassroots linkage, elite orientation) that lead to programmatic alignment. This article extends an emerging research agenda that highlights how social movements shape party politics and offers evidence that niche party-movement interactions open new avenues for political representation counterbalancing mainstream parties' increasing detachment from civil society.Niche parties, political parties that focus on limited programmatic appeals regarding issues that are not easily located alongside the traditional, classdominated left/right dimension (Meguid 2005: 347-348), have received increasing attention. These parties have shaped contemporary European politics in important ways, as exemplified by the 2014 Scottish independence referendum backed by the Scottish National Party. Studies have illuminated the interactions between niche and mainstream parties (Meguid 2008; Pardos-Prado 2015), how voters respond to shifts in niche party positions (Adams et al. 2012) and when parties transition between mainstream and niche profiles (Meyer and Wagner 2013). No systematic attention, however, has been paid to the social movement roots that many niche parties have in common. Green parties originated from environmental movements, regionalist movements surrounded the origins of many ethnoterritorial parties, and more recently movements concerned with copyright, privacy and internet-related issues gave rise to Pirate parties. Parties' roots in and interactions with movements