This chapter quantifies the emergence and institutionalisation of public petitioning on an unprecedented scale in terms of the numbers of issues, petitions, and signatures. The decisive breakthrough in terms of the volume of public petitions to the House of Commons occurred in the late 1820s and was driven by a series of mighty mobilisations including anti-slavery and parliamentary reform. The chronology of petitioning in the UK followed a similar pattern as elsewhere, but the volume of public petitions to the Commons was exceptional when placed in historical and comparative context. The data demonstrates that the volume of petitions and signatures was underpinned by organised mass campaigns, but also a ‘long tail’ of petitions on small and medium-scale issues. Comparing signatures with electoral data reveals that, for most nineteenth century, more people petitioned than voted in parliamentary elections. For all the well-documented vitality of episodic election rituals, this chapter demonstrates that petitions to Parliament were the most popular, regular means of interaction between subjects and politicians for much of this period.