They are best read in sequence. I have the ones published by Vintage Books in paperback.
On the outside of the back cover at bottom right corner it says "Kurt Wallander Mystery No. 'X' ". Obviously you start with No. 1 which is called 'Faceless Killers'
Maggie - don't know if that link will work, (if not just copy and paste)but it takes you to the Wallander web site which has a chronological list of titles, and lots more info as well