This manuscript, by an unknown author probably writing at one or several Catholic missions in the 18th century, was found at the College for the Propagation of the Faith in Popayán, New Granada (the Spanish viceroyalty that comprised all or parts of present-day Colombia, Ecuador, Panama, and Venezuela). It consists of 103 pages, most of which are taken up by a glossary of words in the Siona indigenous language with their Spanish equivalents. This part of the work is organized in columns, with the Siona words on the left and their Spanish equivalent on the right, separated by an equal sign. Starting on page 83 are 18 pages of the catechism in Siona, written as a means of indoctrination into the faith, with some concluding pages of further vocabulary. Siona is a Western Tukanoan language, today spoken by only about 550 people in Colombia and Ecuador, making this an important historical record of an endangered language. The manuscript, which is preserved in the National Library of Colombia, has no title page and is in poor condition, with spotting and ink on the reverse of the pages showing through. Another difficulty is presented by the author’s use of some phonetic symbols that have not been definitively interpreted.