THE KNOWLEDGE THAT A POLICE OFFICER MUST HAVE TO EFFECTIVELY FULFILL THE POLICE FUNCTIONS OF PROTECTION AND CRIME PREVENTION IS NOT LIMITED TO THE PRACTICAL REQUIREMENTS OF HIS ASSIGNMENT. AN OFFICER MUST HAVE A THOROUGH GRASP OF THE ENTIRE SUBJECT OF LAW ENFORCEMENT AS IT OPERATES WITHIN THE GUARANTEES OF THE UNITED STATES CONSTITUTION. BEFORE INITIATING ANY ENFORCEMENT ACTION, AN OFFICER MUST HAVE PROBABLE CAUSE FOR HIS ACTION AND MUST KNOW WHAT CONSTITUTES PROBABLE CAUSE. THE CASE OF OHIO V. TERRY (1966) INDICATES THAT OFFICERS MAY SEARCH FOR WEAPONS IN CONNECTION WITH A VALID INQUIRY, BUT IT EMPHASIZES THAT COURTS WILL RULE ON THE PROPRIETY OF THE POLICE ACTIVITIES IN EACH CASE BASED ON ITS UNIQUE FACTS. ADDITIONAL DECISIONS OF THE COURTS SUPPLY GUIDANCE TO THE POLICE BY SETTING THE LIMITS OF PERMISSIBLE CONDUCT DURING ARRESTS, WHILE OBTAINING CONFESSIONS, AND WHILE CONDUCTING SEIZURES OF PROPERTY. THE PROCEDURES FOR OBTAINING A SEARCH WARRANT, SEARCHING A STOPPED CAR, AND REGULATING PUBLIC ASSEMBLIES ARE REVIEWED. COMMENTARY IS OFFERED CONCERNING THE POLICE FUNCTION IN RELATION TO THE CITIZENS' RIGHTS OF SPEECH AND PRIVACY. GRAPHICS ARE PROVIDED. (TWK)