This project aims to improve our current understanding of Basque historical phonology by incorporating recent advances in theories of phonetically based sound change, contact linguistics and phonological typology and by using state-of-the-art quantitative and experimental techniques. The new approach is to combine the historical-comparative method with phonetic detail and quantitative typological data for studying the historical sound patterns of a language isolate such as Basque, in which the comparative method finds most difficulties. This project will result in a better understanding of sound patterns that have been subject of discussion for years in Basque historical phonology, and it will advance our knowledge of general typologies of sound change with a thorough analysis of the uncommon sound changes that will be studied. The areas of interest cover the evolution of the opposition between /h/ and /h~/ (only documented in two other languages), changes in the phonetic cues underlying the opposition between the two stop series (from [spread glottis] to voicing), changes in the place of articulation of sibilants, the evolution of vowel inventories, and changes in the accentual system (from phrasal pitch accent to word-level systems, based on pitch or stress depending on the dialect). For each topic under study, the employed methodology will combine philological work comparing the dialectal variants attested in older stages of the language and analysis of acoustic and articulatory data. In cases in which the precise phonetic realization of a given segment has not been described, varieties of interest will be found in the literature in order to obtain acoustic and physiological data encompassing all relevant phonological contexts in the field. Then, precise phonetic information will be extracted from field recordings. Differences regarding age-group will be explored whenever there is evidence for a sound change in progress. Experiments will be devised to find coarticulatory patterns that might have yielded sound change in the past, including analyzing reconstructed sequences that are not found in the modern language (e.g. #st-) as pronounced by speakers of modern Basque. The project methodology will also include other data-based approaches, such as computer-based segment co-occurrence searches of big corpora to find potential biases in the phonotactic distribution of the segments under study and searches for typological parallels of each process. The role of contact will be assessed by looking for convergent evolutions in neighboring languages. The long-term significance of the project lies in contributing to the reconstruction of the phonology of Proto-Basque as well as to both typologies of phonetically based sound change and sound change in situations of linguistic contact. An indirect and major benefit of the project is that it will provide a new methodology for the study of the historical phonologies of language isolates.