NINE-ONE-ONE HAS BEEN ADOPTED BY THE TELEPHONE INDUSTRY AS A NATIONWIDE NUMBER FOR EMERGENCIES. CALIFORNIA OPERATING STANDARDS REQUIRE THAT ALL PUBLIC SAFETY ANSWERING POINTS (PSAP) OR 911 ANSWERING CENTERS, ANSWER ALL CALLS WITHIN 10 SECONDS, OPERATE 24 HOURS A DAY, 7 DAYS A WEEK, AND GIVE ONLY 1 BUSY SIGNAL PER 100 CALLS IN BUSY TIMES. TECHNICAL STANDARDS REQUIRE A MINIMUM OF TWO 911 TRUNK LINES PER PSAP, EMERGENCY POWER SOURCES, AND NO-COIN 911 CALLING FROM PUBLIC PHONE BOOTHS. PSAP OPERATORS MAY RESPOND TO 911 CALLERS BY DISPATCHING EMERGENCY AID DIRECTLY, OR RELAYING THE INFORMATION TO THE PROPER PUBLIC SAFETY AGENCY, TRANSFERRING THE CALL, OR REFERRING THE CALLER TO A SEVENDIGIT PHONE NUMBER. DECENTRALIZED AND CENTRALIZED 911 SYSTEMS COVERING SEVERAL CITIES ARE DESCRIBED. IN PLANNING A 911 SYSTEM. COOPERATION BETWEEN JURISDICTIONS AND PUBLIC SAFETY AGENCIES IS ESSENTIAL. PLANNING CHECKLISTS INCLUDE IDENTIFYING PARTICIPATION AGENCIES, FORMING PLANNING TASK FORCES, LOCATING THE PSAP, DECIDING THE MODE OF PSAP RESPONSE, DECIDING UPON EQUIPMENT, AND OTHER ACTIVITIES. COST ESTIMATES MUST INCLUDE TELEPHONE COMPANY CENTRAL OFFICE 911 SWITCHING, TRUNKS AND LINES, PSAP EQUIPMENT AND PERSONNEL, PUBLIC SAFETY AGENCY COSTS, AND MANY OTHERS. A FORMAT FOR ALL 911 PLAN SUBMISSIONS IS DISCUSSED. TABLES, CHARTS, REFERENCES, AND A GLOSSARY ARE INCLUDED.