Electronic interceptions appeared as early as 1900, during the Boer War of 1899–1902. The British Royal Navy had … See more

The United States Department of Defense has defined the term "signals intelligence" as:
1. A category of intelligence comprising either individually or in combination all communica… See more

A collection system has to know to look for a particular signal. "System", in this context, has several nuances. Targeting is the process of developing collection requirements:
"1. An intelli… See more

COMINT (communications intelligence) is a sub-category of signals intelligence that engages in dealing with messages or voice information derived from the interception of foreign communications. COMINT is commonly r… See more

Electronic signals intelligence (ELINT) refers to intelligence-gathering by use of electronic sensors. Its primary focus lies on non-communications signals intelligence. The Joint Chiefs of Staff define it as "Technical … See more

Signals intelligence and measurement and signature intelligence (MASINT) are closely, and sometimes confusingly, related. The signals intelligence disciplines of communications and electronic intelligenc… See more

Since the invention of the radio, the international consensus has been that the radio-waves are no one's property, and thus the interception itself is not illegal. There can, however, be national laws on who is allo… See more