This dissertation presents new models and algorithms for the Vanpool Assignment problem. A vanpool is typically a group of nine to fifteen passengers who share their commute to a common target location typically an office building or corporate campus). Commuters in a vanpool drive from their homes to a park-and-ride location. The driver of the vanpool drives a van to the park-and-ride location while the other members of the vanpool drive their own vehicles and then board the van at the park-and-ride location. The driver drives the entire group to the target location and then drives the group back to the park-and-ride location at the end of the work day. The Vanpool Assignment problem studied in this dissertation is motivated by a program offered by Gulfstream Aerospace, a large employer in the Dallas/Fort-Worth area, Dallas Area Rapid Transit DART), and Enterprise Rent-A-Car. The objective function of the first model presented in this study is to minimize the total cost of a one-way trip to the target location for all employees at a particular location including those employees who opt-out of the program and choose not to join a vanpool). This model, called the Minimum Cost Vanpool Assignment Model MCVAM), utilizes constraints on the capacity of each van and quality-of-service constraints on the cost and travel time involved in joining a vanpool. The second model, which is based on the first model, maximizes the number of employees who join vanpools. Both of these models allow only one-stop park-and-ride vanpooling. The third model, called the Two-Stop Minimum Cost Vanpool Assignment Model TSMCVAM), is a different form of the first model that allows up to two park-and-ride locations per vanpool rather than just one. The fourth model is based on the third model and maximizes the number of employees who join vanpooling while allowing vanpools to stop at up to two park-and-ride locations. In the computational results presented in this study, the first model and the second model produced competitive vanpool assignments. However, these assignments dont include some of the potential vanpoolers because of park-and-ride limitations and also because of the distances to the park-and-ride locations used. The third and the fourth models allowed up to two park-and-ride locations per vanpool and attracted more customers, which in turn increased the overall fill rate of vans. The two-stop method also reduced the overall vanpooling costs significantly by taking advantage of the expanded customer base. However, the solution times for these models, even in medium size problem sets, were significantly longer than the solution times for the one-stop models. Solution times for the first and the second model for a small scale problem are fast, and it is observed that these models were scalable to a larger size problem. However, solution times for the third model were significantly longer on the smallest scale problem set. When the larger problem sets were introduced to evaluate the scalability of these models, it was apparent that getting a solution close to optimal may take days or even weeks. It is obvious that there is a need to solve larger size problem sets faster to take full advantage of the two-stop models. In order to derive high quality solutions in reasonable time limits, heuristics are developed to solve the two-stop models for larger-scale problem sets. First, we introduce the Incumbent Solution Heuristic, which uses the MCVAM solution as an incumbent solution for the TSMCVAM. Secondly, we present the Restricted Allowance Heuristic, which restricts the possible two-stop passenger park-and-ride combinations by removing combinations that are unlikely to be used in an optimal solution. Thirdly, we describe a Linear-Programming-based LP) heuristic called the Relaxed Restricted Allowance Heuristic. This heuristic utilizes the Integer-Programming-based IP) Restricted Allowance Heuristic as the starting point. The Relaxed Restricted Allowance Heuristic uses the LP-based solution to gain information on the IP problem to be able to further restrict the solution space and possibly reduce the solution time. Lastly, we introduce the Greedy Cover Heuristic GCH), which picks a minimal set of two-stop park-and-ride combinations to accommodate as many passengers as possible. On the largest problems 600 potential passengers and 120 park-and-ride locations), the GCH is found to be the best of these heuristicsï¼› it produces optimality gaps ranging from 5.38% to 9.45% with an average optimality gap of 7.84% in CPU times ranging from 1 minute to 15 minutes and 9 seconds with an average of 6 minutes and 6 seconds. We claim three main contributions with this dissertation: 1. Introduction of the MCVAM: the literature focuses on carpooling and related shared-vehicle transportation models. To the best of our knowledge, this is the first mathematical programming model proposed for the standard one-stop) vanpool assignment problem. 2. Introduction of the TSMCVAM: the MCVAM models the current practice in vanpooling of using one park-and-ride location per vanpool. However, the TSMVCAM can generate significant cost savings compared to the MCVAM with little or no increase in trip times for most passengers by allowing vanpools to stop at a second park-and-ride location. 3. Heuristics that can find high-quality solutions to the TSMCVAM with reasonable CPU times.