I saw this on one of the US Boards, and it looked like fun.
Basically someone picks a them, and you go through the alphabet letter by letter naming one item. The person who has Z, picks the next theme.
For example: Theme for 1st round is musical artists.
So I'd put
A is for Aerosmith
Next person would put
B is for Beatles etc.
Then when someone does the Z, they would put new theme (fruit, animals whatever), and we start again...:-x