The use of Internet technology for solicitation by sex workers has raised important legal and regulatory questions. We provide a description of the new institutions that facilitate prostitution online, and their potential market effects. We then supply some of the first evidence on several key parameters of interest to policymakers. First, we find that workers who solicit online largely represent growth in the overall prostitution market, as opposed to simple displacement of the off-line, street-focused market, although we find sizeable displacement effects among sex workers in their 30s and 40s. Using a newly-implemented survey, we also find that most sex workers who solicit online engage in lower-risk behaviors than traditional street-based workers; however, workers close to the margin for migration from outdoor work bring riskier business and sexual practices with them as they enter the off-street-sector.