user86: Wikipedia's article on the fifty-move rule states:

All of the basic checkmates can be accomplished in well under 50 moves. However, in the 20th century it was discovered that some positions of certain endgames can only be won in more than fifty moves (without a capture or a pawn move). The rule was changed to include certain exceptions in which one hundred moves were allowed with particular material combinations. However, more and more exceptions were discovered and in 1992 FIDE abolished all such exceptions and reinstated the strict fifty-move rule.

I have never seen an example of this, though I used to think the K, N, B vs. K ending was one.  When is it possible to force a win in 50 moves or more, but not less than 50 moves?

user27150: A more comprehensive list of endgames sorted by the number of moves it could take to mate (based on Nalimov tablebases) is at http://kirill-kryukov.com/chess/longest-checkmates/longest-checkmates-sorted-by-length.shtml
These vary in length from 1 move to 262 moves.  It does not include the mate in 549 because that endgame has 7 pieces on the board and the tablebases only include positions with up to 6 pieces on the board.
As for KBN vs. K, that can be done in 33 moves.

user12: Yes, there are quite a few endgames that require more than 50 moves with best play from the defender.
Wikipedia has a list of material imbalances where it could take more than 50 moves depending on the specific position.  Here are a few examples:

Rook and bishop vs lone rook (often a draw though)
Two bishops vs a lone knight 
Two knights vs a lone pawn (the defender must have a pawn)
Four knights vs a lone queen (would never happen over the board…)
Queen and rook vs queen and rook
Two queens vs two queens


86: <p>Wikipedia's article on the <a href="http://en.wikipedia.org/wiki/Fifty-move_rule" rel="nofollow noreferrer">fifty-move rule</a> states:</p>
<blockquote>
<p>All of the basic checkmates can be accomplished in well under 50 moves. However, in the 20th century it was discovered that some positions of certain endgames can only be won in more than fifty moves (without a capture or a pawn move). The rule was changed to include certain exceptions in which one hundred moves were allowed with particular material combinations. However, more and more exceptions were discovered and in 1992 FIDE abolished all such exceptions and reinstated the strict fifty-move rule.</p>
</blockquote>
<p>I have never seen an example of this, though I used to think the <a href="https://chess.stackexchange.com/q/59/86">K, N, B vs. K ending</a> was one.  When is it possible to force a win in 50 moves or more, but not less than 50 moves?</p>
 27150: <p>A more comprehensive list of endgames sorted by the number of moves it could take to mate (based on Nalimov tablebases) is at <a href="http://kirill-kryukov.com/chess/longest-checkmates/longest-checkmates-sorted-by-length.shtml" rel="nofollow noreferrer">http://kirill-kryukov.com/chess/longest-checkmates/longest-checkmates-sorted-by-length.shtml</a></p>
<p>These vary in length from 1 move to 262 moves.  It does not include the mate in 549 because that endgame has 7 pieces on the board and the tablebases only include positions with up to 6 pieces on the board.</p>
<p>As for KBN vs. K, that can be done in 33 moves.</p>
 12: <p>Yes, there are quite a few endgames that require more than 50 moves with best play from the defender.</p>

<p><a href="http://en.wikipedia.org/wiki/Endgame_tablebase#Endgame_theory" rel="noreferrer">Wikipedia</a> has a list of material imbalances where it could take more than 50 moves depending on the specific position.  Here are a few examples:</p>

<ul>
<li>Rook and bishop vs lone rook (often a draw though)</li>
<li>Two bishops vs a lone knight </li>
<li>Two knights vs a lone pawn (the defender <em>must</em> have a pawn)</li>
<li>Four knights vs a lone queen (would never happen over the board…)</li>
<li>Queen and rook vs queen and rook</li>
<li>Two queens vs two queens</li>
</ul>
