This thesis is dedicated to glottalisation in Scottish Gaelic, recorded in various south-western dialects. Glottalisation has been reported to occur, optionally or inconsistently, between a stressed short vowel and another vowel, in hiatus or with an intervening consonant, but not in svarabhakti groups. Less commonly, it is found in other contexts, for example, after a long vowel. It has been described either as glottal stop or a period of creaky phonation. This thesis presents the results of an analysis of two types of primary sources – the dialectological materials (word lists) collected in the mid-20th century as part of the Survey of the Gaelic dialects of Scotland, and the audio recordings of native speakers made about the same time in different areas by the School of Scottish Studies. The data obtained from the SGDS records was expected to help determine the geographical area in which glottalisation occurs, its frequency in particular dialects, and the phonological contexts in which it occurs in these dialects. A closer examination of various types of examples, considering other related linguistic phenomena (such as epenthesis), was expected to answer the question of the phonological status of glottalisation in Gaelic dialects. The audio recordings were used for phonetic analysis aiming to provide a phonetic description of Gaelic glottalisation, and to find out whether it is related to other prosodic phenomena, such as stress and pitch.