The fire investigator must be prepared through study and constant review of fire causes and effects. Needed equipment must be in working condition and available. The investigator's objective at the fire scene is to determine the cause of the fire. In case the fire is found to be arson, care must be taken to ensure that evidence is collected in a legally acceptable manner. Interviews with firefighters and other witnesses to the blaze can be of assistance in determining the point of origin, duration of burn, rate of burn, and possible causes. After all possible accidental or natural causes have been eliminated, the demands of an arson investigation are in effect. The investigator must systematically collect, mark, preserve, and subsequently present all evidence of an incendiary fire. A daily log of all case activities should be kept and reports written immediately. Notes should be kept in case the investigator should be called to testify. Where specialized expert knowledge is required to interpret evidence, the investigator should solicit the necessary help from professionals in the appropriate fields such as electricity, natural gas, and chemistry. If possible, the prosecutor should be involved during the investigation, and prior to trial, there should be a conference with the prosecutor to review case presentation in court. The investigator should be thoroughly prepared for a court appearance, and the information provided should be scientific and presented in a professional manner. Two footnotes and eight bibliographic entries are provided.