This book investigates the changes that affected vowel length during the development of Latin into the Romance languages and dialects. In Latin, vowel length was contrastive (e.g. pila "ball" vs. pila "pile", like English bit vs. beat), but no modern Romance language has retained that same contrast. However, many non-standard Romance dialects (as well as French, up to the early 20th century) have developed novel vowel length contrasts, which are investigated in detail here. Unlike previous studies of this phenomenon, this book combines detailed historical evidence spanning three millennia (as attested by extant texts) with extensive data from present-day Romance varieties collected from first-hand fieldwork, which are subjected to both phonological and experimental phonetic analysis. Professor Loporcaro puts forward a detailed account of the loss of contrastive vowel length in late Latin, showing that this happened through the establishment of a process which lengthened all stressed vowels in open syllables, as in modern Italian casa ['ka:sa]. His analysis has implications for many of the most widely-debated issues relating to the origin of novel vowel length contrasts in Romance, which are also shown to have been preserved to different degrees in different areas. The detailed investigation of the rise and fall of vowel length in dozens of lesser-known (non-standard) varieties is crucial in understanding the development of this aspect of Romance historical phonology, and will be of interest not only to researchers and students in comparative Romance linguistics, but also, more generally, to phonologists and those interested in historical linguistics beyond the Latin-Romance language family.