THE DECISION TO EMPLOY DEADLY FORCE IS UNQUESTIONABLY THE MOST DIFFICULT CHOICE A POLICE OFFICER EVER MAKES. ELEMENTS OF THE PROCESS INVOLVED IN REACHING THE DECISION, REFERRED TO AS PEDA, INCLUDE PERCEPTION, EVALUATION, DECISION, AND ACTION. ALTHOUGH THE PROCESS OCCURS IN A SPLIT SECOND, IT IS USEFUL TO IDENTIFY EACH ASPECT OF THE PROCESS. DURING THE PERCEPTION PHASE, THE OFFICER FORMS A MENTAL SET REGARDING THE SITUATION. PERCEPTION IS A PRODUCT OF SUCH FACTORS AS INFORMATION RECEIVED THROUGH POLICE COMMUNICATIONS, THE OFFICER'S SENSES OF VISION AND HEARING, CITIZEN INFORMATION, PROFESSIONAL KNOWLEDGE AND SKILLS, AND PERSONAL ATTITUDINAL BIAS. EVALUATION REFERS TO THAT PHASE DURING WHICH THE OFFICER MENTALLY COMPARES HIS PERCEPTION OF THE IMMEDIATE SITUATION WITH SEVERAL IMPORTANT CRITERIA INCLUDING THE APPLICABLE STATE AND DEPARTMENTAL GUIDELINES, IMMEDIATE RISKS OF HARM, AND AVAILABILITY AND POTENTIAL EFFECTIVENESS OF ALTERNATE METHODS OF HANDLING THE SITUATION. THE DECISION TO USE DEADLY FORCE INVOLVES NOT ONLY THE ACTUAL COMMITMENT TO USE IT, BUT ALSO THE MANNER IN WHICH IT WILL BE EMPLOYED. THE FINAL COMPONENT OF THE PROCESS, THE ACTION PHASE, INVOLVES THE ACTUAL USE OF DEADLY FORCE. UNDER COMMON LAW, A POLICE OFFICER MAY LEGALLY USE DEADLY FORCE AS A LAST RESORT IN INSTANCES OF SELF-DEFENSE OF THREATENED DEATH, PREVENTION OF THE UNLAWFUL KILLING OF ANOTHER, PREVENTION OF THE COMMISSION OF A FELONY, AND UNDER OTHER SPECIFIED CIRCUMSTANCES. SOME STATES AND MANY POLICE DEPARTMENTS SPECIFY A MORE RESTRICTIVE POLICY REGARDING USE OF DEADLY FORCE; IT IS IMPERATIVE THAT THE OFFICER UNDERSTAND SUCH POLICIES. A SKETCH ILLUSTRATES THE TEXT, AND FOOTNOTES ARE INCLUDED. (LWM)