This book proposes that phonological contrast, in particular the robustness of a phonemic contrast, does not depend solely on the presence of minimal pairs, but is instead affected by a set of phonetic, usage-based, and systemic factors. This perspective opens phonology to a more direct interpretation through phonetic analysis, undertaken in a series of case studies on the Romanian vowel system. Both the synchronic phonetics and morpho-phonological alternations are studied, to understand the forces that have historically shaped and now maintain the phonemic system of Romanian. A corpus study of phoneme type frequency in Romanian reveals marginal contrasts among vowels, in which a sharp distinction between allophones and phonemes fails to capture relationships among sounds. An investigation of Romanian /I/ provides insight into the historical roots of marginal contrast, and a large acoustic study of Romanian vowels and diphthongs is a backdrop for evaluating the phonetic and perceptual realization of marginal contrast. The results provide impetus for a model in which phonology, phonetics, morphology and perception interact in a multidimensional way.