The phonetics-phonology interface has long been debated; some linguists argue for a modular approach (Keating 1984, Pierrehumbert 1990, Zsiga 1997, Cohn 1998), while others argue that there is no interface, and that phonetics and phonology are one and the same (Browman & Goldstein 1989-1992, Ohala 1990). Recent proposals by Gafos (2002), and Petrova et al. (2006) have proposed that language-specific phonetic differences, such as the timing of articulatory gestures and the implementation of a two-way voicing contrast in stops, are grammatically controlled through constraints on gestural alignment and laryngeal features. These proposals blur the line between the two components by including language-specific phonetic facts within the phonological grammar. This dissertation investigates the phonology-phonetics interface by documenting and analyzing data from Turkish and Urban East Norwegian, both cited by Petrova et al. (2006) and Bradley (2007). The results of a production study in each language and one perception study in Turkish demonstrate that the data do not pattern as previously described, or as predicted to occur by these proposals. Results demonstrate that Norwegian coalescence of "r+coronal" sequences (producing a retroflex consonant), and voicing assimilation within words in Turkish pattern as categorical processes. However, devoicing of word-initial stops in Turkish is non-neutralizing, and vowel intrusion/deletion for "r+non-coronal" sequences in Norwegian is not a categorical process (Kristoffersen 2000, Bradley 2007), but rather gradient and dependent on morphological, consonantal and prosodic context. The gradience across contexts is best captured through a coupled-oscillator model of gestural timing (Nam & Saltzman 2003), while the task-dynamic phonetics implements this coordination of gestures. The data from both languages are best captured if the phonology accounts for complete neutralizations by making qualitative featural changes, while a task-dynamic phonetics produces a gradient quantitative acoustic signal. This dissertation, then, argues for a modular approach to the phonetics-phonology interface, following Keating (1984), Pierrehumbert (1990), Zsiga (1997), Cohn (1998), in that the phonology manipulates features and segments, and a separate language-specific phonetic component interprets features and produces gestural timing patterns. The universal task-dynamic phonetics, then, operates on this output, causing gradient and quantitative changes to articulatory trajectories and the acoustic output. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]