It is the goal of this paper to consider how phonetics may interface with phonology. The role phonetics plays in phonological analysis is considered with respect to features, segments, phonological processes, and the abstractness of phonological solutions. Phonetic evidence is reviewed concerning the feature [strident] that questions the defining properties of this feature, its place in the distinctive feature framework, and its role in the analysis of natural classes for fricatives. The extent to which a sound segment is analyzed as a single unit or a cluster is considered with reference to prenasalized stops in Moru. The phonetic data are neutral with respect to the unitary or complex status of such segments, suggesting that the decision is more properly a phonological one. Phonetic evidence for the phonological process of neutralization is reviewed. Acoustic analysis of word-final devoicing in German, Polish and Catalan provides support for the reality of the process of neutralization in phonological solutions. Finally, phonetics helps provide a set of constraints or limiting conditions on the abstractness of phonological solutions. While phonetics cannot inform phonology about the appropriateness of a particular underlying form, there should be some phonetic transparency between the underlying form and its ultimate phonetic instantiation.