The Time zone history section below hasn't kept up with recent changes, but the following paragraphs and the first table are correct as of March 2010.

Macquarie Island is changing its time zone from UTC+10 with DST to UTC+11 year-round.

South Australia has extended its daylight saving period to match the neighboring states.

Western Australia adopted daylight saving time during its summers for a trial period running from 2006-12-03 to 2009-03-29. The first transition was in December, because their debate came too late for an October start. Subsequent transitions were in October. The trial was not popular and will not be continued.

The Commonwealth Games were held in Melbourne in March 2006. To minimize the disruption, Australian states that observed DST were asked to extend it from March 26 to April 2. They all complied.

Rules currently in force

Notes:
Ashmore and Cartier Islands have no permanent residents. They are administered from Northern Territory, but (when people are present) they observe Western Australian Time.
Coral Sea Islands Territory has no permanent residents, except at a weather station on Willis Island. The tz database has no information about the territory. It uses Queensland Time.
Lord Howe Island and the nearby Ball's Pyramid are remote islands administered as part of New South Wales.
Macquarie Island is part of Tasmania, and used Tasmanian Time until 2010-04. After then it will remain on UTC+11, matching Tasmanian summer time.
Broken Hill, New South Wales, and nearby places observe South Australian Time. The tz database describes this area as "Yancowinna County". Yancowinna County seems to be obsolete, but here is an old map  (PDF) of it.
There is an unofficial time zone, locally referred to as Central Western Australia Time, halfway between Central and Western. This area maintained UTC+8:45 all year round until December 2006, when Western Australia began to observe DST. Now it, too, observes DST, setting its clocks to UTC+9:45 in the local summer. It consists of a few very small towns along the south coast where South Australia meets Western Australia, including Border Village, Eucla, Madura, and Mundrabilla.
Giles Meteorological Station (25°2'S, 128°17'E), in Western Australia, is reported to observe South Australian Time.
Narrabri Shire, New South Wales, was reportedly planning to remain on the regular last-Sunday-in-October transition for 2000, even though the rest of New South Wales had advanced the date to the last Sunday in August as a concession to the Sydney Olympics.

Time zone history

Source: This information was adapted from the tz database. Zone names come from that database. The names don't necessarily match any names used in the "real world".

Example: When it was 14:18 (or 2:18 p.m.) local time on 2000-09-03 (September 3, 2000) in Wollongong, Australia, what was the UTC?

Wollongong is in the state of New South Wales. From the first table, New South Wales is in the Australia/Sydney time zone. (This is a specialized meaning of "time zone", which is more precise than common usage.) In the second table, look in the block of rows for Australia/Sydney. Among them, look for the first row on which the Final Date exceeds 2000-09-03 14:18. You find that the third line has a date of "Present", which is the first to exceed 2000. Looking across the row, the AN rule applies, and standard time is UTC+10. Finally, look in the third table under the AN rule. Once again, find the date range that includes the date in question (2000-09). That would be the first range, "2000-08 to 2001-03". This rule says that daylight saving time was in effect from 02:00 [a.m.] of August 27, 2000 to 03:00 of March 25, 2001 for Wollongong. The date in question does in fact fall between those two dates, so daylight saving time was in effect. Therefore, the local time was standard time plus one hour, or UTC+11. Subtract eleven hours from the given time to get UTC. The answer is 2000-09-03 03:18 UTC.

Note: The Holiday Islands are a resort area off the Pacific Coast of Queensland. Whitsunday Island is the largest of them. The Holiday Islands Zone comprises Hayman (20°03'S, 148°53'E), Lindeman (20°27'S, 149°02'E), and Hamilton (20°22'S, 148°57'E) Islands.

Time zone names

According to the Australian National Standards Commission, the official names and abbreviations for Australian time zones are:

The tz database uses the following time zone names and abbreviations for Australian time zones. They were chosen on the basis of information received from Australian residents. That information has been called into question.

Sometimes Eastern Summer Time is called "Eastern Standard Summer Time", with ESST as its abbreviation. Still more rarely, you may see Central Standard Summer Time or CSST. The tz database invented the abbreviation LHST for Lord Howe Island Standard Time.