This year's theme is "The Gadgeteers" and is illustrated by Julian Beresford.   It will run from 9th July into September and the challenge is for each child to read 6 books in that period. 

The children get various rewards after every 2 books read and a certificate at the end of the challenge, once they have completed their 6 books. 

There is much more information at Summer Reading Challenge including suggested reading lists and other activities.