It has been observed by many writers on English phonetics that /p/, /t/, /k/ and /tʃ/ are frequently glottalized, i.e. produced with closed glottis. This observation raises a variety of interesting questions. Firstly, the phonological environments in which glottalization occurs have yet to be satisfactorily described; a preliminary attempt at a re-statement was made in Roach (1973) and a fuller account presented in Roach (1978). Secondly, it is of interest to study the articulatory mechanisms used in the production of glottalization, both from the point of view of finding out more about how laryngeal closures in speech are produced, and also with respect to the temporal organization of the laryngeal and supralaryngeal closures. Thirdly, since the incidence of glottalization (and of the closely related phenomenon of glottal replacement) appears to vary according to geographical and social factors, age and sex, it is of interest in dialectological and sociolinguistic studies of English. Finally, in a wider context, glottalization may be studied as being potentially an on-going sound change in English, and as a phenomenon that might possibly be linked with similar laryngeal articulations in other languages, e.g. the stød of Standard Danish and of West Jutland Danish.