Cheapest priced copy (Revised Edition): $1.79 at Card Kingdom, near mint, their price list as of .
Library of Leng 
Artifact · Uncommon · Fifth Edition · #387
You have no maximum hand size.
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.
Legal inCommanderLegacyVintagePauper
Not legal inBrawlStandardPioneerModern
14 printings · $1.79 to $299.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Unlimited Edition | 258 | Uncommon | $11.99 | — |
| 30th Anniversary Edition | 254 | Uncommon | $16.99 | — |
| 30th Anniversary Edition | 551 | Uncommon | $74.99 | — |
| Revised Edition | 261 | Uncommon | $1.79 | — |
| Fourth Edition Foreign Black Border | 333 | Uncommon | — | — |
| Fourth Edition | 333 | Uncommon | $1.79 | — |
| Fifth Edition | 387 | Uncommon | $2.29 | — |
| Collectors' Edition | 258 | Uncommon | $12.99 | — |
| Intl. Collectors' Edition | 258 | Uncommon | $16.99Out of stock | — |
| Foreign Black Border | 261 | Uncommon | — | — |
| Limited Edition Alpha | 257 | Uncommon | $299.99 | — |
| Limited Edition Beta | 258 | Uncommon | $129.99 | — |
| Special Guests | 158 | Mythic | $10.99 | $12.99 |
| Summer Magic / Edgar | 261 | Uncommon | — | — |
9 rulings from Wizards of the Coast
- 4 October 2004You can look at a randomly discarded card before deciding where it goes.
- 4 October 2004The ability replaces the normal discard action with a discard action that puts the card on the library instead of the graveyard.
- 4 October 2004The discard triggers anything else that triggers on discards.
- 4 October 2004The ability applies any time a spell or ability has you discard as part of its effect. It does not matter if you or your opponent control the spell or ability. The discard is forced because it is an effect.
- 4 October 2004You can't use the Library of Leng ability to place a discarded card on top of your library when you discard a card as a cost, because costs aren't effects.
- 4 October 2004If more than one card is discarded due to a single effect, the Library allows you to decide whether or not to use it on each of the cards. You get to decide the order the cards are placed on the library if more than one goes there.
- 4 October 2004This effect has no effect on the cards being put into the graveyard from a library, because they are not "discarded".
- 4 October 2004Since the card goes directly to the library, the card is not revealed unless the spell or ability requiring the discard specifically says it is.
- 1 October 2009If multiple effects modify your hand size, apply them in timestamp order. For example, if you put Null Profusion (an enchantment that says your maximum hand size is two) onto the battlefield and then put Library of Leng onto the battlefield, you'll have no maximum hand size. However, if those permanents entered in the opposite order, your maximum hand size would be two.