Hayley Wood is a 51.7-hectare (128-acre) biological Site of Special Scientific Interest south-east of Great Gransden in Cambridgeshire. It is a Nature Conservation Review site, Grade 1, and it is managed by the Wildlife Trust for Bedfordshire, Cambridgeshire and Northamptonshire. It was the subject of a book by the academic and woodland expert Oliver Rackham, listed below, who regularly visited and recorded his observations of the woodland in his notebooks.