This study examines a major linguistic event underway in New York City. Of its 10 million inhabitants, nearly a third are speakers of Spanish. This community is socially and linguistically diverse: Some speakers are recent arrivals from Latin America while others are lifelong New Yorkers. Some have origins in the Caribbean, the historic source of Spanish in NYC, while others represent a more recent wave of immigration from mainland Latin America. Communities in both regions differ substantially in their speech, exhibiting wide-ranging variability in how they use the phonological, syntactic, and lexical resources of Spanish. Currently in NYC, these varieties exist in a state of sustained contact with each other. Spanish speakers in NYC also interact with and use different varieties of English. Not since the colonial settlement of Latin America has a contact event of such scale and diversity taken place in Spanish. The current project examines this situation from the perspective of sociolinguistics, studying the variable production of the phoneme /"s"/ in the speech of twenty Spanish speakers who vary along a continuum of exposure to NYC. Variation in the pronunciation of /s/ has been instrumental in understanding how Spanish has changed over time, how it spread from the Iberian Peninsula to Latin America, and how different groups of speakers use the language today. Traditionally, variation in /s/ production has been studied from a categorical perspective, relying on the perceptual coding of three segmental variants: [s], [h] ("s-aspiration"), and [Ø] ("s-deletion"). Recent developments in the acoustic analysis of speech suggest that this method can be substantially improved. This project brings the study of /s/ variation in line with modern practices of acoustic science by developing descriptive methods that are sensitive to differences in a range of continuous parameters, including those related to the temporal and spectral properties of fricatives. Such parameters provide a means for examining sociolinguistic variation from a gradient perspective, offering insights into patterns of language use that are observable only at the "sub" segmental level. The project produces results relating to (1) the advantages of acoustically based methods of analysis, and (2) Spanish spoken in NYC. With respect to methods, analysis of 4,800 cases of phonological /s/ reveals patterns that are opaque at the segmental level. Results show that all speakers gradiently weaken /s/ in certain phonetic contexts. Second, data challenge the level of internal homogeneity presumed to be present in national varieties of Spanish. Within national groups, substantial differences in speech are present. Regarding the contact situation in NYC, data suggest that sustained interaction among speakers of different dialects is promoting a trend of convergence: Among recent arrivals from Latin America significant differences in the acoustic properties of /s/ emerge along regional lines. Those with Caribbean origins produce s with a significantly shorter duration (in milliseconds) and lower "center of gravity" (in Hz) than those with Mainland origins. This regional difference is greatly attenuated in the speech of long-time residents of New York. These findings are consistent with current research suggesting that dialect contact is promoting the formation of a New York City Spanish speech community. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]