This dictionary describes Tocharian A, one of two Tocharian languages documented in manuscripts of Buddhist texts from the second half of the 1st millennium CE, excavated in the oases of the Tarim basin. The dictionary contains also a thesaurus, based on all the identified texts in Tocharian A, including previously published and unpublished texts from various collections (Paris, Berlin). All forms of words, including variants occurring in the texts, are listed separately with reference to all occurrences and a sample of passages in transcription and translation. The meaning of a number of words has been better defined and, when necessary, corrected against previous glossaries. Much focus has been laid on phraseology and literary parallels with other Buddhist texts in Sanskrit and Uighur. The description of the verbal forms has been listed according to the stems of the paradigms. The sources of loanwords, e.g., from Tocharian B, Old and Middle Indo-Aryan, Iranian, Old Turkic, and Chinese, as well as the corresponding words in Tocharian B, are also given. (2 further parts in preparation.)