Growing concerns about global motorization and climate change have led to increasing interest in sustainable transportation alternatives such as bikesharing (the shared use of a bicycle fleet). Since 1965, bikesharing has grown across the globe on five continents: Europe, North America, South America, Asia, and Australia. Today, approximately 100 bikesharing programs are operating in an estimated 125 cities, with more than 139,300 bicycles. Bikesharing's evolution is categorized into three generations: (a) white bikes (or free bike systems), (b) coin-deposit systems, and (c) information technology-based systems. In this paper, a fourth generation is proposed: demand-responsive, multimodal systems. A range of existing bikesharing business models (e.g., advertising) and lessons learned are discussed, including (a) bicycle theft and vandalism, (b) bicycle redistribution, (c) information systems (e.g., real-time information), (d) insurance and liability concerns, and (e) prelaunch considerations. Although limited in number, several studies have documented bikesharing's social and environmental benefits, which include reduced auto use, increased bicycle use, and a growing awareness of bikesharing as a daily mobility option. Despite bike-sharing's ongoing growth, obstacles and uncertainty remain: these include future demand, safety, sustainability of business models, limited cycling infrastructure, challenges to integrate with public transportation systems, technology costs, and user convenience (e.g., limited height adjustment on bicycles, lack of cargo space, and exposure to weather). More research is needed for a better understanding of bikesharing's effects, operations, and business models in light of its reported growth and benefits.