Until 2015, we knew very little about the work and workers in the sharing/on-demand economy. Indeed, the last official government survey of the broader contingent workforce was conducted in 2005 -- long before most of these new platforms or apps even existed. However, in the last year, our understanding has advanced dramatically, thanks to the release of a few key pieces of research, including: the JPMorgan Chase Institute study, "Paychecks, Paydays and the Online Platform Economy;" Lawrence Katz and Alan Krueger's "The Rise and Nature of Alternative Work Arrangements in the United States, 1995-2015;" work by Intuit and Emergent Research, "Dispatches from the New Economy: The On-Demand Economy Workforce;" and others. However, while these and other studies have revealed a great deal about the work and workers in the sharing/on-demand economy, there is still much we need to understand. This paper aims to lay out what we know about the sharing/on-demand economy and define questions for additional research. This paper is meant to be a resource for public and private research organizations, foundations, government agencies, and other parties interested in promoting a more thorough understanding of the sharing/on-demand economy workforce, including its relationship to the broader contingent workforce.