The electromagnetic (EM) environment of an item of equipment is the totality of all of the electromagnetic disturbances that exist at its operational location. It is generally becoming more ‘polluted’, due to increased use of electronic technologies, especially wired data communications, wireless communications, and switch-mode power conversion. Every telecommunication-service-bearing equipment makes use of some part of the radiofrequency (RF) spectrum which is a natural but scarce national resource. Ineffective management of the spectrum results in electromagnetic interference (EMI) in which either telecommunication systems are susceptible to service disruption from other services, or they themselves serve as sources of service disruption to other systems. The paper enumerates the causes and sources of EMI as well as its disruptive effects on systems such as Global Positioning Systems, aircraft and medical devices. Various means of mitigating the effects of EMI or protecting equipment against EMI are also discussed.