Elder Dragon Highlander is a Magic: The Gathering variant which provides a way of encouraging casual, interactive games with a low barrier to entry while still requiring good deck building skills. It can be played 1-on-1 but is usually multiplayer.
A forum for discussion of the rules, strategy, and changes to EDH can be found here: http://edh.truespace.ca/EDH_Forum/ - - -This page details the "official" rules common to most groups.

An EDH deck must contain at least 100 cards, including the general.

Players must choose a legendary creature as the "General" for their deck, in advance, and check with the coordinator of the whichever group they will be playing with. No two players may have the same general in the same game, and no player may have anyone else's general in their deck. Allocation of generals is first come, first serve. Within a given group, generals are preserved between meetings/games so that one's deck can remain consistant. Your general must have at least three colours in his mana cost.

The general's mana cost dictates what mana symbols may appear on cards in the deck. A deck may not generate mana outside it's colours; anything which would generate mana of an illegal colour generates colourless mana instead.

You must have at least 10 spells of each colour of your general in your deck. Multicolour spells (e.g. Boros Guild Mage) count for both of the appropriate colours.

Example: If you were play Phelddagrif (Casting cost 1UWG) as your General, your deck may not contain any red or black cards; no card in such a deck may contain red or black mana symbols or hybrid mana symbols (Talisman of Dominance, Life//Death and Boros Guildmage are not allowed. Degavolver is doubly bad).

EDH is played with (vintage_legal) cards, with the exception that cards are legal as of their set's prerelease.

No two cards in the deck may have the same english name with the exception of basic lands

No sideboard/wishboard is allowed

All Core and Expansion sets Legal for Vintage are Legal, from Alpha thorugh to the current printing of the Core Set; As EDH is a casual format, Cards from Collectors Editions (Gold Border Backs), Special Release Decks (Black Variant Backs, Gold Borders) and all promo release cards are allowed.

Information on the banned list for Elder Dragon Highlander can be found here:
csclub.uwaterloo.ca/~geduggan/EDH_rules.html

• Rofellos, Llanowar Emissary
• Zur, The Enchanter

• Players begin the game with 40 life.
• If a player suffers 21 points of *combat* damage from a single general, they lose. This is an additional state based effect, similar to poison counters, but separate and specific to each general. This damage cannot be healed or retroactively removed, even if the creature is removed from play.
• All generals are removed from the game and placed in the General Zone before shuffling at the start of the game.
• While a general is removed from the game, it may be played. As an additional cost to play your general this way, you must pay +{2} for each previous time you have played it this way.
• If a general would be put into a graveyard from anywhere, or removed from the game it's owner may place it in the General Zone instead. (This is a replacement effect.. if chosen, the creature never goes to the graveyard and will not trigger abilities on going to the graveyard).

• Karakas's ability does not return a General to its owner's hand.
• Rune Tail, Kitsune attendant flips when his controller's life total is [60] or higher.

All "house rules" in above paragraphs are highlighted in italics and blue. In addition there are further house rules:

• Russ Davies is maintaining the list of local generals on the manascrew.co.uk website.
• House Rule: The general is in the "General Zone" when he is not in play or a graveyard.#
• After each game, any player may propose a general or card for the banned list. A simple roll call of "Ays" and "Nays" is used, and if a 2/3 majority is found for the ban, it is banned. In the same way, any player may propose the removal of a banned card or general.

• Dromar, The Banisher - Julian Parker.
• Crosis, The Purger - Paul Murphy
• Treva, The Renewer - Ryan Brierley
• Garza Lol, Plague Queen - Peter Oxley
• Merieke Ri Berit - Russ Davies
• Vorosh The Hunter - Chris Moss
• Doran The Siege Tower - Mark Hammond
• Teneb, The Harvester - Chris Stockton
• Sol'Kanar the Swamp King - Joe Davis
• Sliver Overlord - Brian Davis
• Oros, The Avenger - Steve Pennington