Cognitive radio is being intensively researched as the enabling technology for license-exempt access to the so-called TV White Spaces (TVWS), large portions of spectrum in the UHF/VHF bands which become available on a geographical Fan Shop - Oilers - Jerseys basis after digital switchover.Both in the US, and more recently, in the UK the regulators have given Model Kits conditional endorsement to this new mode of access.This paper reviews the state-of-the-art in technology, regulation, and standardisation of cognitive access to TVWS.It examines the spectrum opportunity and commercial use cases associated with this form of secondary access.