Measurement and signature intelligence (MASINT) is a technical branch of intelligence gathering, which serves to detect, track, identify or describe the distinctive characteristics (signatures) of fixed or dynamic target sources. This often includes radar intelligence, acoustic intelligence, nuclear intelligence, and chemical and biological intelligence.

MASINT is defined as scientific and technical intelligence derived from the analysis of data obtained from sensing instruments for the purpose of identifying any distinctive features associated with the source, emitter or sender, to facilitate the latter's measurement and identification.

MASINT specialists themselves struggle with providing simple explanations of their field. One attempt calls it the "CSI" of the intelligence community, in imitation of the television series CSI: Crime Scene Investigation.

Another possible definition calls it "astronomy except for the direction of view." The allusion here is to observational astronomy being a set of techniques that do remote sensing looking away from the earth (contrasted with how MASINT employs remote sensing looking toward the earth). Astronomers make observations in multiple electromagnetic spectra, ranging through radio waves, infrared, visible, and ultraviolet light, into the X-ray spectrum and beyond. They correlate these multispectral observations and create hybrid, often "false-color" images to give a visual representation of wavelength and energy, but much of their detailed information is more likely a graph of such things as intensity and wavelength versus viewing angle.

MASINT may have aspects of intelligence analysis management, since certain aspects of MASINT, such as the analysis of electromagnetic radiation received by signals intelligence, are more of an analysis technique than a collection method. Some MASINT techniques require purpose-built sensors.

MASINT was recognized by the United States Department of Defense as an intelligence discipline in 1986. MASINT is technically derived intelligence that—when collected, processed, and analyzed by dedicated MASINT systems—results in intelligence that detects and classifies targets, and identifies or describes signatures (distinctive characteristics) of fixed or dynamic target sources. In addition to MASINT, IMINT and HUMINT can subsequently be used to track or more precisely classify targets identified through the intelligence process. While traditional IMINT and SIGINT are not considered to be MASINT efforts, images and signals from other intelligence-gathering processes can be further examined through the MASINT discipline, such as determining the depth of buried assets in imagery gathered through the IMINT process.

William K. Moore described the discipline: "MASINT looks at every intelligence indicator with new eyes and makes available new indicators as well. It measures and identifies battlespace entities via multiple means that are difficult to spoof and it provides intelligence that confirms the more traditional sources, but is also robust enough to stand with spectrometry to differentiate between paint and foliage, or recognizing radar decoys because the signal lacks unintentional characteristics of the real radar system. At the same time, it can detect things that other sensors cannot sense, or sometimes it can be the first sensor to recognize a potentially critical datum."

It can be difficult to draw a line between tactical sensors and strategic MASINT sensors. Indeed, the same sensor may be used tactically or strategically. In a tactical role, a submarine might use acoustic sensors—active and passive sonar—to close in on a target or get away from a pursuer. Those same passive sonars may be used by a submarine, operating stealthily in a foreign harbor, to characterize the signature of a new submarine type.