Transportation-network companies such as Uber and Lyft have permeated cities around the world. While they have been lauded for introducing a new mobility option, questions of equity have been raised, including in relation to people with disabilities. Numerous lawsuits have been filed against Uber and Lyft for lack of disabled accessibility of transportation service they facilitate, with some of the lawsuit focusing on wheelchair accessibility. These have been reported in the media while work on the topic is lacking in the academic literature. This doctoral research explores wheelchair accessibility in transportation hailed through Uber and Lyft in the U.S., with a partial focus on the phenomenon in Washington, DC. The study sought to gain insight into wheelchair-accessibility matters with respect to four main stakeholders - riders, companies, drivers, and regulators and other government agencies. The purpose was a) to deepen understanding on the topic based on a holistic approach to core issues and produce evidence-based knowledge and b) to provide policy recommendations where needed. A mixed-methods approach was used to investigate the research problem. The quantitative strand surveyed 341 wheelchair users in the U.S., while the qualitative strand consisted of three sets of 16 qualitative interviews with drivers on the Uber and Lyft apps, Uber and Lyft company representatives, and representatives of relevant government agencies in Washington, DC. The study finds the following: 1) The service might be filling a transportation gap for some wheelchair users even though it is a two-tiered system that disadvantages motorized-wheelchair users. 2) The challenges surrounding wheelchair accessibility are perceived differently by the stakeholders and as a result there are differing views of how to solve them. 3) Overcoming inaccessibility challenge needs to involve changes on both Uber and Lyft and government agencies. Uber and Lyft and government agencies will find this study of interest to help them appreciate other stakeholders' perspective and use the findings to support policy decisions. / Doctor of Philosophy / Transportation-network companies connect drivers who are interested in providing a ride to riders who are looking for transportation through smartphone apps. Uber and Lyft are the most common of these companies. Both companies operate in many cities around the world. They are praised for creating a transportation alternative, but there is a concern that they may not serve everyone equally. For example, people with disabilities, especially wheelchair users have complained that they are not receiving the same service as those who do not use wheelchair. In the US, there are numerous lawsuits have been filed against Uber and Lyft for lack of disabled accessibility. Some of the lawsuit focus on wheelchair accessibility. These issues are reported in the media mostly. This doctoral research looks at wheelchair accessibility in transportation hailed through Uber and Lyft in the U.S., with a partial focus on the phenomenon in Washington, DC. The study sought to gain insight into wheelchair-accessibility matters with respect to four main stakeholders - riders, companies, drivers, and regulators and other government agencies. The purpose was a) to deepen understanding on the topic based on a holistic approach to core issues and produce evidence-based knowledge and b) to provide policy recommendations where needed. A survey and a set of interviews were used to investigate the research problem. The study finds the following: 1) The service might be filling a transportation gap for some wheelchair users even though it is a two-tiered system that disadvantages motorized-wheelchair users. 2) The challenges surrounding wheelchair accessibility are perceived differently by the stakeholders and as a result there are differing views of how to solve them. 3) Overcoming inaccessibility challenge needs to involve changes on both Uber and Lyft and government agencies. Uber and Lyft and government agencies will find this study of interest to help them appreciate other stakeholders' perspective and use the findings to support policy decisions.