Professor Rackham's observations of woodland and the landscape were made principally in two sets of notebooks: one red, one blue. In these, he made handwritten entries recording his observations, sometimes adding small sketches. These notebooks contain the raw data on which he drew when writing his books. However, historical and antiquarian notes on the British landscape which Rackham collated from a variety of sources were kept in separate folders, labelled according to county and location. These also form part of the Rackham collection now kept at Corpus Christi College, Cambridge.