Smart city technology is making cities more effective which is necessary for the rapid growth in urban population. With the rapid increase in advanced metering infrastructure and other digital technologies, Smart cities have become smarter with efficient electronic devices and embedded sensors based on the Internet of Things (IoT). This paper provides a comprehensive review of the smart cities concept with its components and applications. Moreover, technologies of IoT used in smart cities infrastructure and some practically implemented smart cities in the world are mentioned as exemplary implementations. Some open issues and future directions concluded the paper.