This dissertation investigates how lexical stress in Spanish is phonetically manifested within the syllable, and how stress manifestation interacts with other prosodic effects, such as phrasal accent and initial word-boundary effects. One of the challenges in the study of prosody is the fact that multiple prosodic factors induce variation in a limited number of phonetic dimensions. For this reason, results in the literature have often been inconclusive or conflicting. The disentanglement of these prosodic effects will help us understand the complex nature of prosody. The results of this study show that stress effects can be identified independently of phrasal level prominence (accent) and prosodic-boundary effects (position in word). Among the prosodic effects, durational and spectral properties clearly differentiate stressed onset and vowel from their unstressed counterparts, but intensity does not. In addition, similarities between stress and accent effects, grouped as `prominence effects', are distinguished from word-level boundary effects that are conditioned by accent conditions. Finally, the results indicate that syllable constituency can be involved in prosodic manifestation, possibly constrained by higher-level prosody, such as isochrony (stress-timed vs. syllable-timed rhythms). We identified apparent complementarity between syllable constituents in the stress manifestation of two dialects of Spanish, which can be attributed to two structural motivations. On the one hand, syllable constituency is involved in segmental variation at the lexical-level (stress); and on the other hand, a higher-level prosody (isochronous rhythm) can play a role as an upper bound in constraining the variability. A gestural account is provided to accommodate the asymmetric contribution of syllable constituents to the temporal manifestation of stress. The investigation of the phonetics of prosody manifestation provides us insight into interrelations among prosodic factors, and the systematicity behind the complexity of prosodic effects. It is hoped that this dissertation contributes to a better understanding of prosody as a well-structured grammatical component, and its connections to segmental phenomena in languages.