This project sets out to discover and develop techniques for the lemmatisation of a historical corpus of the Cornish language in order that a lemmatised dictionary macrostructure can be generated from the corpus. The system should be capable of uniquely identifying every lexical item that is attested in the corpus. A survey of published and unpublished Cornish dictionaries, glossaries and lexicographical notes was carried out. A corpus was compiled incorporating specially prepared new critical editions. An investigation into the history of Cornish lemmatisation was undertaken. A systemic description of Cornish inflection was written. Three methods of corpus lemmatisation were trialed. Findings were as follows. Lexicographical history shapes current Cornish lexicographical practice. Lexicon based tokenisation has advantages over character based tokenisation. System networks provide the means to generate base forms from attested word types. Grammatical difference is the most reliable way of disambiguating homographs. A lemma that contains three fields, the canonical form, the part-of-speech and a semantic field label, provides of a unique code for every lexeme attested in the corpus. Programs which involve human interaction during the lemmatisation process allow bootstrapping of the lemmatisation database. Computerised morphological processing may be used at least to partially create the lemmatisation database. Disambiguation of at least some of the most common homographs may be automated by the use of computer programs.