I don't know where tog's magic number of 32 time zones came from, but it's clearly too small. My best guess at the true current number is 35. Here's how I derived it. There are 25 time zones that are an integral number of hours offset from GMT, ranging from GMT -1200 (Kwajalein) to GMT +1200 (New Zealand). All are in use somewhere (but see comments on Kwajalein below). Here are the 12 other zones described in Olson's usno1989 file; see SunOS 4.x's /usr/share/lib/zoneinfo/usno1989 (why did they remove this info from SunOS 5?): -0930 Marquesas Is; Cook Is; French Polynesia -0330 Newfoundland; -0130 Newfoundland Daylight +0330 Iran +0430 Afghanistan +0530 India; Sri Lanka +0545 Nepal +0630 Myanmar (Burma); Cocos I +0930 South Australia; +1030 South Australia Summer +1130 Norfolk I +1245 Chatham Is That's 10 non-integral zones, so the total number is 25 + 10 = 35. I'm not counting the Arabian peninsula, which (rumor has it) uses solar time, not time zones. Nor am I counting daylight savings time as a separate zone. And no doubt there are some errors in usno1989, so this number is not definitive. abe listed a bunch of time zones like ``Java Time'' that are no longer in use, at least according to usno1989. I think those zones date back to colonial times. Also, usno1989's info for the ex-Soviet Union is woefully out of date due to the March 1991 time zone reforms in the (then-) SU. E.g. I think Uelen is now +1200 (+1300 summer), not +1300 (+1400 summer). Kwajalein is a special case -- it's west of the International Date Line but usno1989 says it's 12 hours behind GMT! Perhaps it's a typo in usno1989, and should be +1200? Or perhaps they prefer being closer to US/Pacific time since they're the target of ICBMs from Vandenberg.