## 1 Introduction  
Before talking about the Internet of Things (IoT), it is worthy to explore the evolution of the Internet. The first experimental network of two computers was created between the TX-2 computer by Lincoln Labs of Massachusetts Institute of Technology (MIT) and the Q-32 mainframe operated by the RAND corporations via a dedicated telephone line in 1965 [1]. The Internet was invented by [PERSON] in 1973 [2]. Commercial use of the Internet started in the late 1980s [1]. The World Wide Web (WWW) was invented by [PERSON] in 1989 [2] and became available in 1991 [3]. The first mobile phone with Internet connectivity was the Nokia 9000 Communicator, launched in Finland in 1996 [4]. Thus, the mobile-Internet was formed. In June 2000, Friends Reunited as the first online social network to achieve prominence in Britain was launched [5]. By emerging social networks, peoples' identities are added to the Internet. In the next step in the IoT, objects can connect and communicate with each other via the Internet. The research in the IoT is in the beginning stages, and researchers provided different definitions for it. Thus, there isn't only one definition for IoT. The IoT is composed of two words: \"Internet\" and \"Thing.\" The \"Internet\" can be defined as \"The interconnection of computers in the world based on TCP/IP protocols\" and the \"Thing\" is \"an object that is not precisely identifiable\" Thus, \"Internet of Things\" semantically means a worldwide network of interconnected objects uniquely addressable, based on Transmission Control Protocol (TCP) and Internet Protocol (IP). Thus, it is reasonable to define the IoT as \"Things having identities and virtual personalities operating in smart spaces using intelligent interfaces to connect and communicate within social, environmental, and user contexts\" [6]. Also, IoT can be defined as a connection of people and things at any time, in any place, with anything and anyone, using any path and any service [7, 8]. This implies addressing elements such as convergence, content, collections (repositories), computing, communication, and connectivity in the context where there is a seamless interconnection between people/humans and things and/or between things (see Figure 1) [9]. Thus, IoT is a huge dynamic global network infrastructure of Internet-enabled physical and virtual objects/entities with web services which contains embedded technologies and all types of information devices such as global positioning system (GPS), infrared devices, scanners, radio frequency identification (RFID) tags/devices, sensors, actuators, smartphones, and the Internet to sense, identify, locate, track, connect, monitor, manage, communicate/interact, cooperate, and control of objects/things in physical, digital, and virtual world. It uses computing and self-configuring capabilities (based on interoperable communication protocols) and software tools to process information, achieve data mining, and extract knowledge. One of the most important applications of IoT is the Smart Grid (SG). SG is a data communications network which is integrated with the power grid to collect and analyze data that are acquired from transmission lines, distribution substations, and consumers. Based on these data, SG can provide predictive information to its suppliers and customers on how to best manage power [10]. In this paper, different layers of IoT architecture will be discussed. We will investigate technologies which are essential to apply IoT to SG. Several IoT applications and services in SG will be introduced. Finally, challenges that must be addressed and future work are discussed. The rest of the paper is organized as follows. In Section 2, IoT, its history and development are reviewed. Smart grid and its components are discussed in Section 3. Section 4 presents how IoT can be used in SG to accomplish reliable data transmission. The architecture of IoT is discussed in Section 5. In Section 6, several key technologies to enable applying IoT to SG are introduced.