This book is an attempt to define the concept of metrical foot in acoustic terms. The foot constituent has been approached from various theoretical standpoints. Little attention, however, has been devoted to its empirical justification. The author explores the possiblity that the foot is a purely vocalic constituent and can be described as a complex network of inter- and intravocalic relations between duration, pitch and intensity. He argues that a number of quantitative processes, like pre-fortis clipping or final lengthening, are inexplicable without reference to the foot. Convincing arguments are provided for the vowel-based isochrony which is derivative of the quantitative processes operating within the foot. The author also points out ways in which these empirical results may be incorporated into phonological theory.