—Precise and accurate localization is one of the fundamental scientific and engineering technologies needed for the applications enabling the emergence of the Smart World. Localization techniques became popular with the Global Positioning System (GPS) for outdoor applications, and in recent years, this has been followed by Wi-Fi localization for indoor applications. More recently, localization science and technology has progressed into in-body medical applications. Localization technologies have their own specific challenges depending on the application and environment, which are left for scientists and engineers to overcome. This paper presents the relation among different elements of the Smart World and corresponding localization technologies, classifies localization applications enabling smart devices and environments into logical categories, describes the complexity of the technologies used for localization, and introduces some of the open challenges for localization in the sm...