Parliamentary efforts to facilitate wider participation and specialised online platforms have made petition instruments more attractive and relevant, yet comparisons of petition instruments are rare. This article examines formalised (parliamentary petitions) and non-formalised petition instruments (online petitions) in Austria via a cluster analysis of actors and content of 600 petitions between 2011 and 2018. We find that, depending on the legal and institutional design, different petition instruments serve three different democratic functions: voice in parliament, link with constituents and public mobilisation. Complementing these results with insights from expert interviews with petitioners, the article provides also an understanding of how petition instruments affect petitioners’ motivations. Our findings yield a more nuanced picture of the motivations and functions of petition instruments.