One of the principal criteria whereby the Apachean languages may be divided into two main sub-stocks is the development of Primitive Athapaskan *t. This sound is retained in Navaho, San Carlos, Chiricahua, and Mescalero, but becomes k in Jicarilla and Lipan (thus falling together with PA *k) and k (before the vowels a and o) or č (before the vowels e and i) in Kiowa-Apache. The purpose of this paper is to describe the phonetic circumstances attendant upon these shifts, circumstances which illustrate rather well the relationship between phonetic change—changes in sound-producing habits which do not alter the phonemic system of a language—and phonemic change. Changes in the pronunciation of PA *t have probably taken place in all the Apachean languages, but in only three of these languages (viz. Jicarilla, Lipan, and Kiowa-Apache) have the changes resulted in a disturbance of the phonemic system.