The chapter begins with an overview of current Hausa phonology. It then provides a picture of what existed in ‘Old Hausa’ and the subsequent changes that took place, many due to regular sound laws such as Klingenheben’s Law, the Law of Codas in Reduplication, loss of word-final nasals, and the change of non-initial /r/ into /y/. Although sporadic, historical metathesis was much more common than one usually finds in diachronic change. Glottal stop and /h/ are newly introduced phonemes, resulting from the addition of onsets to vowel-initial words. The high frequency glottalized semivowel /’y/ is also a new phoneme resulting from the fusion of /?/ + /y/. Gemination was originally absent but appeared later and became common through phonological and morphological means. Vowels developed from a skewed 2-3-5 (initial-medial-final) system, with vowel length only distinctive medially, into a system with five vowels, all of which now occur long and short. Starting with two level tones, Hausa later developed Falling and Rising contours, the latter having simplified to High. The loss of vowels resulted in the existence of lexical floating tones not underlyingly attached to segments.