Hand

A player's hand consists of cards that have been drawn, but not played. It is one of six zones of the game. Flavor-wise, the hand represents the conscious mind of the player as a planeswalker and the starting hand is the first seven items that occur to you when you begin a duel with another planeswalker. The starting hand may be reduced when a mulligan is performed. After the optional mulligan, it is called your opening hand.

Rules

From the Comprehensive Rules (June 7, 2024—Modern Horizons 3)

• 402. Hand
  • 402.1. The hand is where a player holds cards that have been drawn. Cards can be put into a player’s hand by other effects as well. At the beginning of the game, each player draws a number of cards equal to that player’s starting hand size, normally seven. (See rule 103, “Starting the Game.”)
  • 402.2. Each player has a maximum hand size, which is normally seven cards. A player may have any number of cards in their hand, but as part of their cleanup step, the player must discard excess cards down to the maximum hand size.
  • 402.3. A player may arrange their hand in any convenient fashion and look at it at any time. A player can’t look at the cards in another player’s hand but may count those cards at any time.

No maximum hand size

There are some cards that grant you no maximum hand size. Some of them are:

• Spellbook ().
• Graceful Adept ().
• Library of Leng (). Also has "If an effect causes you to discard a card, discard it, but you may put it on top of your library instead of into your graveyard."
• Reliquary Tower. Also has ": Add to your mana pool."
• Thought Vessel (). Also has ": Add to your mana pool."
• Venser's Journal (). Also has "At the beginning of your upkeep, you gain 1 life for each card in your hand."
• Kruphix, God of Horizons (). Also has "Indestructible; If unused mana would empty from your mana pool, that mana becomes colorless instead."
• Tamiyo, the Moon Sage (). Granted as an emblem.