The first crossword puzzle, in the modern sense, appeared in a Sunday copy of the New York World on December 21, 1913.

The modern crossword is made of a number of interlocking words within a frame of black and white squares. Each word corresponds to a numbered clue.

Before this, puzzles had included square puzzles in which letters spelled the same word horizontally and acrostics in which a series of answers laid out one above the other would reveal another related word running vertically.

There are now many variations on crossword puzzles.

*Another type of popular puzzle is the jigsaw puzzle. This is a picture which is printed onto cardboard and then cut into many pieces. These pieces interlock so that you can recreate the picture.