This chapter presents a radio transmitter as a main source of EMI emissions and electromagnetic (EM) disturbances, including the classification and types of EMI in radio systems, both narrowband and broadband EMI. Additionally, this chapter describes the nonlinearity of a power transmitter amplifier as a significant cause of electromagnetic disturbances and EMI, which the transmitter emits. Furthermore, a communication receiver is herein considered the main victim of EMI and disturbances emitted from transmitters of other radio communication networks and own network. The critical parameters for the RX EMI immunity are considered in this chapter, such as the RX selectivity, sensitivity, gain, and dynamic range, as well as the level of RX intermodulation distortions, RX IQ imbalance, and Rx equivalization. Additionally, radio transmission over random multipath channels is described and numerically illustrated through the symbol error rate (SER) for several random channel distributions, such as the Rayleigh, Ricean, and Nakagami Gamma distributions. Finally, impulse EMIs in radio channels and their impact on data transmission are also considered.