Ensuring onboard passenger comfort on buses is essential, as it significantly impacts the overall quality of public transit services. Onboard comfort is a multidimensional concept, encompassing attributes such as vibrations, load factor, driving style, and noise, and is a critical component of service quality. Its evaluation is vital for public transport companies, offering insights into continuous monitoring, assessment, and developing strategies to improve services. In recent years, increasing attention has been devoted to bus comfort, focusing on the attributes to be measured and the methods employed. However, as far as the authors know, systematic investigations into studies on on-board comfort remain limited. This paper consolidates existing knowledge by reviewing studies published between 2006 and 2024, retrieved using PRISMA’s methodological approach and leading scientific repositories (Scopus, Web of Science, and Google Scholar). The review examines how comfort is influenced by factors such as speed, onboard accelerations and vibrations, driving style, road design, and surface roughness. It also considers studies assessing in-vehicle noise, crowding, and thermal comfort. The reviewed studies are categorized into three measurement approaches: objective, subjective, and mixed. The latter integrates subjective methods (e.g., surveys and questionnaires) with objective techniques (e.g., acceleration data collected via accelerometers or smartphones) and defines indicators that combine passengers’ perceptions with physical and kinematic parameters measured onboard. This review summarizes the current state of research, offering a comprehensive understanding of onboard comfort and supporting future advancements in evaluating and enhancing bus services.