How many 4-letter words are there?

3,903 in the Tournament dictionary, which is the public-domain ENABLE word list. The Broad dictionary adds more.

What is the highest-scoring 4-letter word?

JAZZ at 29 points, counting tile values with no board multipliers.

No. The page shows the 300 highest-scoring; the pages linked below break the full list down by starting and ending letters.

3,903 words are exactly 4 letters long. JAZZ scores highest at 29 points.

Showing the highest-scoring of 3,903 words. The pages linked below split the rest into smaller lists.

The dictionary holds 3,903 words of exactly 4 letters. A selection is below, ordered by Scrabble value.

Lengths span 4 to 4. The middle of that range is where the words are: 3,903 of them are 4 letters long.

If you are playing for score, JAZZ at 29 points is the pick. It tops both tables: 31 in Words With Friends as well.

The full 4 letters are used by JAZZ, FIZZ and FUZZ.

If you need a narrower cut, the pages linked below split this set by letter and by length.

How many 4-letter words are there?: 3,903 in the Tournament dictionary, which is the public-domain ENABLE word list. The Broad dictionary adds more.
What is the highest-scoring 4-letter word?: JAZZ at 29 points, counting tile values with no board multipliers.
Are all of them listed here?: No. The page shows the 300 highest-scoring; the pages linked below break the full list down by starting and ending letters.