A word puzzle in which the object is to change one word into another by changing one letter at a time into a different letter.

Generally the goal is to change them in as few steps as possible. For instance, changing PORT into WINE can be done in four steps:

   P O R T
1. P O R E
2. P O N E
3. P I N E
4. W I N E

This is clearly the minimum for this change since each letter must be changed at least once. If a letter is the same in the initial and final words, it is possible for the minimum to be less than the length of the word.

Word ladders where it is possible to accomplish the change in the theoretical minimum number of steps become boring quickly, since there are very few possible words to consider; the only steps allowed are ones which swap a letter from the starting word for a letter from the ending word. In the example above, the first word could only have been WORT, PIRT, PONT, or PORE. Only two of these are words, so you can eliminate the others and repeat the process from here. If you do so, you'll find another ladder PORT-WORT-WORE-WIRE-WINE and maybe others.

The more interesting ones require more steps than the theoretical minimum because the words don't exist to do it in the minimum. For example, the change from FLOOR to BROOM looks possible in three steps, but actually requires four steps, because none of "bloor", "froor", and "floom" are real words. The extra step is inserted by changing one of the letters to a different letter (not the one it needs to end up being), then continuing from there. For instance, you could solve this one with the letter D as an intermediate, by the sequence FLOOR-FLOOD-BLOOD-BROOD-BROOM.

When the consonant/vowel patterns of the words to be linked by the ladder are highly different, ladders can require many steps to resolve them. Note that a ladder between two words that each have two vowels, but in different positions, must involve a word with either one or three vowels, since you can only change one letter at a time. What's the shortest change from EDDY to WHIP?