Narrowband-Internet of Things (NB-IoT) is a standard-based low-power wide-area network (LPWAN) technology developed to connect a wide range of new IoT devices and services. The NB-IoT will improve the power consumption of user devices, system capacity, and spectrum efficiency. It is able to be loaded by major mobile equipment and module manufacturers, and indeed it will be existing to be adaptable with any cellular mobile network’s generations. It also benefits from all the security and privacy features of mobile networks. In this chapter, fundamental key aspects of NB-IoT are investigated and the features of NB-IoT and technical properties are proposed in addition to the theoretical concepts. A detailed overview of the current NB-IoT-related technologies such as Long-Term Evolution for Machines (LTE-M), Third Generation Partnership Project (3GPP), enhanced Machine Type Communication (eMTC) and ultralow power technologies is discussed. This chapter will also provide details of different applications related to NB-IoT such as smart grid, smart cities, and smart industry. Security issues and other deployment considerations will be explored. © 2020 Elsevier Inc. All rights reserved.