This is an experimental phonetic investigation into the vowel duration system of Civili, an indigenous language spoken in Gabon and some of its neighboring countries. Apart from providing insight into how mother-tongue speakers articulate and perceive certain vowels, it contributes significantly to the establishment of a credible orthography for this language. Speech data acquired through extensive fieldwork were analyzed acoustically to determine sound qualities, after which perception tests were administered to determine how listeners perceive vowel sounds in different environments. The findings are of significance for linguistic descriptions per se, as well as for eventual use in the field of human language technologies. This seven-chapter book is mainly intended for an expert readership and for students of phonetics and phonology.