Ε-petitions, the digital version of printed petitions, are increasingly being used as complimentary means of nonconfrontational, online citizen mobilization/protest. They attract considerable research interest because they provide (big) data to study e-petitioning and the political and other aspects of socio-spatial issues. E-petition studies lack discussion of ontology, of “what is an e-petition,” implicitly treating e-petitions as “systems-as-a-whole” or, seldom, as relational formations. Acknowledging the foundational role of ontology, Assemblage Thinking (AT) is argued to beget a more judicious approach when e-petitions are employed as research instruments to study the “who-what-when-where-and-how” of a socio-spatial issue and, concurrently, their situated contribution to issue-related decision-making. After presenting the reductionist/essentialist and the nonreductionist/relational approaches to the study of e-petitions and introducing ΑΤ, an assemblage-based framework is proposed that conceptualizes e-petitions as multiplicities comprising assemblages, dynamic compositions emerging from processes of heterogeneous components coming together to serve a purpose. A concomitant methodology is outlined and an illustrative example is offered. The advantages of assemblage-based over reductionist/essentialist approaches for the situated co-analysis of socio-spatial issues and e-petitions are discussed, indicating how they address prominent concerns of the literature, and future research directions are suggested.