The study is based upon three hypotheses: (1) a pyro firesetter sets a fire in a public portion of the building, without regard to the consequences to the occupants, usually using available materials as the plant and rarely using a flammable liquid; (2) a revenge firesetter usually starts a fire at night, in an occupied apartment, in the bedroom and uses a flammable liquid; and (3) a vandal firesetter usually sets a fire in a public portion of the building using available combustibles. Motives and other information about the fires and the firesetters were obtained through the Fire Marshall's official report. Data were cross-tabulated by computer to compare the relationships between seven firesetting motives (pyromania, revenge, vandalism, insurance fraud, welfare fraud, psycho, and crime concealment) and a number of variables such as place of fire origin, area of origin, point of origin, object set on fire, use of flammable liquid, etc. From the data results, typologies were established for the different types of firesetters. However, because the samples are small and are only representative of those firesetters caught and arrested, the value of this research lies in its reminder that arson investigations should be distributed to those investigative agencies best suited to arson cases. Tables and footnotes appear throughout. A bibliography of 19 references is included, and a coded data sheet and a chart of arson behavior taxonomy are appended.