The Internet of Things (IoT) is the most significant technology in smart cities—those that use numerous technologies—and has been highlighted as a means of improving transport, energy, and healthcare. Although research has often focused on how IoT technologies can be applied to enhance infrastructure in smart cities, more studies are needed to clarify how they should be used. Therefore, this literature review not only explores the existing effectiveness-enhancing applications of these technologies in smart cities but also discusses the challenges and issues (e.g., privacy and security) of implementing IoT in such cities. The insights from this review indicate future directions for how IoT technologies can be implemented in smart cities while addressing opportunities and challenges.