Sets released: Urza's Legacy, Sixth Edition, Urza's Destiny, Portal:
  Three Kingdoms, Starter, Mercadian Masques

Major changes:

  - Sixth edition was a pretty complete rethink of the whole timing system
  and card templating, ending up with the 'Grand Unified Timing System'
  - No more batches, interrupt windows, damage prevention bubbles,
  pre-series, phase abilities or phase costs.
  - No more interrupt or mana source cards, these can be played as
  instant cards under the new system.
  - The stack was introduced.
  - The term 'fast effect' was dropped from the rules.
  - The term 'pseudospell' was dropped from the rules.
  - The concept of setting up a prevention or replacement shield was
  introduced.
  - The term 'bury' was dropped from Magic vocabulary.
  - The term 'successfully cast' was dropped as well.
  - The ability 'haste' was introduced and the term 'summoning sickness'
  was dropped.
  - No more summon cards, replaced with creature cards instead.
  - Creature cards with multiple-word creature types now count as each
  separate creature type individually, with many older types being
  hyphenated.
  - No more 'fizzle', replaced with 'countered on resolution'.
  - No more 'cast', replaced with 'play'.
  - No more 'total mana cost', replaced with 'converted mana cost'.
  - Triggered abilities never resolve at the pauses during a spell,
  they all use the stack and resolve independently.
  - Players lose from having 0 life almost immediately, rather than
  waiting until the end of the phase.
  - Combat became a phase of its own.
  - Combat damage uses the stack.
  - Protection no longer absorb all trample damage, as the damage 
  assignment ignores the protection ability.
  - Tapped blockers now deal combat damage, they previously didn't.
  - Tapped artifacts don't automatically turn off; Howling Mine, Static
  Orb and Winter Orb got errata to preserve their turning off behaviour.
  - The end of turn step / until end of turn wear-off distinction is
  introduced.
  - The Oracle was introduced.
  - The core set has its own expansion symbol as of Sixth Edition.

  - Urza's Legacy introduced premium (foil) cards.
  - Urza's Legacy also marked a trend for effects that tap or untap
  something to change from only being "target creature, artifact or land" 
  to "target permanent"

Trivia:

  - No cards with trample were printed in Sixth Edition.

Some parts © 2009 Advameg, Inc.