Speculative endeavours contributes to an emerging field of scholarship that focuses on alternative forms of knowledge production and speculation in nineteenth century US-American society. It sheds light on unofficial knowledges such as insider information, rumour, gossip, slander, emphasising how knowledges excluded by institutional discourses and authorities form a core part of the developing market economy. Ranging from the Early Republic to the Gilded Age, contributions analyse entanglements of financial, cultural, and social capital. They focus on social actors who differ from the newly minted ideal of the (free, white, male) entrepreneurial individual. The speculative endeavours discussed include illicit communications located in slave quarters and domestic spaces, communal interventions into a commercialised print market, debates on immigrant fiduciary and legal competency, and disciplinary techniques of pecuniary pedagogy. Taken together they offer unprecedented interdisciplinary insights into an emerging age of capital.