Ufology is the study of the UFO phenomenon. At its core is the investigation of UFO reports as made by human witnesses, the enigmatic source of the original sighting typically having long since departed. In some cases, however, physical traces may have been left on the environment and these need to be collected and analyzed according to accepted scientific procedures. Primary witnesses need to be interviewed and other corroborating witnesses (and data) sought out. Since well over 90 percent of all UFO reports turn out to be IFOs -- Identified Flying Objects -- after a thorough examination, it is important to ascertain if any mundane phenomena, manmade, meteorological or astronomical, may have been in the immediate vicinity of the sighting and somehow served as its stimulus. Everything from street lamps and advertising blimps, to ball lightning and the planet Venus have been misinterpreted as UFOs at one time or another. Only by identifying and eliminating such mundane sources can researchers concentrate on the core phenomenon. With close encounters and other so-called "high strangeness" cases, a thorough investigation is even more necessary, especially where episodes of "missing time" and other psychological or physiological effects are reported by the witness(es). Indeed, a UFO investigation can become quite complicated, involving issues of ethics, confidentiality, media relations and other aspects of human behavior with which most of us are ill-equipped, or at least untrained, to deal with. Questions about regressive hypnosis, potential hoaxes, witness reliability and so on tax even the most sincere and objective investigator. Accordingly, MUFON has established a program to train member volunteers as Field Investigators. The heart and soul of this program is the MUFON Field Investigator's Manual, now in a newly revised fifth edition. This 311-page manual comes bound in a sturdy 3-ring loose-leaf folder and includes instructions for investigating a variety of UFO phenomena. Whether you decide to join MUFON and undertake the training program or not, the Field Investigator's Manual contains a wealth of information and is an indispensable tool for undertaking your own investigations.