A study of Dakota Sioux presents evidence for Possessor Ascension. In this construction, a nominal that is semantically a possessor is syntactically not a constituent of the noun phrase but a constituent of the clause. The report first discusses the universal characterization of Possessor Ascension in the framework of relational grammar, and describes ways in which Possessor Ascension is expressed in Sioux. Next, four arguments for this construction are presented. One is based on verb agreement, the second on reflexivization, the third on the distribution of the possessive morpheme, and the fourth on the morpheme /ki-/. Certain constraints on this construction are examined. The effect of Possessor Ascension on verb agreement is seen as being of particular importance because it constitutes a strong argument against a frequently cited form of the verb agreement rule in Sioux based on semantic notions. It is concluded that there are two types of Possessor Ascension in Dakota Sioux. The first follows the Host Limitation Law and is optional. The second type is ascension of a possessor to level 3 followed by advancement to 2. This type is obligatory and occurs only when the noun being possessed is alienable. A 28-item bibliography is included. (MSE)