The use of metal organic frameworks (MOFs) as heterogeneous photocatalysts is critically reviewed. First we revisit the general assumption of MOFs behaving truly as semiconductors, demonstrating that such semiconducting behaviour only occurs in a very limited subset of materials. Further, the main approaches for efficient light harvesting and active site engineering in MOF-based photocatalysts are discussed. Finally, the main advantages of MOFs as photocatalysts and the challenges that need to be addressed in order to improve catalytic performance are evaluated.