In recent years, the concept of a “smart city” has emerged as a new approach to providing high-quality amenities to city residents by dynamically optimizing resource use. Convenient amenities and services are smart cities enhance residents’ quality of life in the areas of healthcare, transportation, energy use, and education. With the growth of modern cities and the emergence of the Internet of Things (IoT), Blockchain can serve as a fundamental technology with a wide range of applications in smart cities. There are two objectives for this essay. To assist academics who wish to make a contribution to this rapidly and steadily expanding topic, it first provides a comprehensive summary of the body of research on blockchain applications in smart cities. It also identifies patterns and makes recommendations for future lines of inquiry. The review’s conclusions demonstrate the sharp rise in recent years in the quantity of articles devoted to the research of blockchain applications and smart cities, but the study also names some of the most important pieces in this subject. We also highlighted the security concerns with blockchain-based IoT applications, particularly in light of blockchain technology’s limitations. The academician and researcher will use this study to improve the IoT-based Blockchain application. This chapter provides an introduction to blockchain technology, smart cities, complex events, the Internet of Things, and other technologies. It also discusses how blockchain technology is crucial for protecting apps from fraudulent users. Additionally, it explores several methods for incorporating Blockchain into IoT applications for smart cities as well as the difficulties this presents.