Wireless communications are mainly limited by the properties of radio channels, i.e. wireless channels. Wireless signals experience severe distortions in delays, amplitudes, phases, and many other aspects, and the distortions vary significantly with time, frequency, and location of the communications. Furthermore, there are other limiting factors such as system bandwidth and radiation power allowed. Therefore, wireless channels are transient, unreliable, and error prone. Wireless communications have a broadcast nature, and excessive interference in the network will cause deterioration in network performance and waste network energy and spectrum resources. A wireless channel observed by a transceiver pair is affected by both the link performance and also the network interference environment. Therefore, radio resource management and interference management are necessary in wireless networks to improve channel qualities of all users in the network and to provide acceptable QoS to users. There are many mechanisms for radio resource and interference management. Medium access control and power control are the most important ones as they grant users channel access rights and determine how different users may affect the communications of each other. In the following chapters, we will introduce the most basic concepts of wireless channel properties and modeling, wireless transceiver design, and classical existing MAC protocols to facilitate understanding of the rest of book. For readers familiar with these concepts, please skip the following discussions and move on to Part II.