Problem definition: We study electric vehicle (EV) sharing systems and explore the opportunity for incorporating vehicle-to-grid (V2G) electricity selling in EV sharing. Academic/practical relevance: The problem involves complex planning and operational decisions, as well as multiple sources of uncertainties. The related optimization models impose significant computational challenges. The potential value of V2G integration may have far-reaching impacts on EV sharing and sustainability. Methodology: We formulate the problem as a two-stage stochastic integer linear program. In the first stage, we optimize decisions related to service planning, the capacity of parking and charging facilities, EV battery capacities, and EV allocation in each zone under uncertain time-dependent trip demand and electricity prices. In the second stage, for a realized demandprice scenario, we construct a time-and-charging-status expanded transportation network and optimize operations of the shared vehicle fleet, EV battery charging, and V2G selling. We develop Benders decomposition and scenario decomposition approaches to improve computational efficiency. A linear-decision-rule-based approximation approach is also provided to model dynamic operations. Results: Via testing instances based on real-world and synthetic data, we demonstrate the computational efficacy of our approaches and study the benefits of integrating V2G in EV sharing from the service provider, consumer, and socioenvironmental aspects. Managerial implications: V2G integration can significantly increase the profitability of EV sharing and the quality of service. It results in the preference of larger EV fleets and battery capacities, which further leads to various socioenvironmental benefits. The benefit of V2G can still prevail, even with more severe battery degradation and can be more significant when combined with (i) more stringent service levels, (ii) more traffic congestion, or (iii) urban spatial structures with concentrated business/residential areas. V2G integration (complemented by fast charging technology) can also benefit carshare users through improvement in the quality of service.