This is the first catalogue of the surviving correspondence of the important naturalist and scientist, Alfred Russel Wallace (1823-1913), the co-discoverer of evolution by natural selection. It contains records of 5,688 letters arranged chronologically, of which 2,748 were written by Wallace and 2,159 were sent to him. The remaining 781 are third party letters which either pertain to Wallace (e.g. a letter from Richard Spruce to William Jackson Hooker which mentions why Wallace and Bates went their separate ways in the Amazon), or are letters written by Wallace's close relatives which contain information useful to scholars interested in Wallace's life. Note that 6,923 individual documents are catalogued, since a letter may be comprised of several documents e.g. the letter itself, an enclosed manuscript, the envelope etc. In addition to letters which the WCP has obtained copies of, the catalogue also lists letters which the WCP has some information about and are reasonably sure still exist, even if their contents are unknown. For example, letters sold at auction in the last c. 20 years, where only the sender, recipient and date are known.