This dissertation investigates several topics in the morphology, syntax and semantics of the Nez Perce verb and verbal clause. The first part of the dissertation focuses on the morphological segmentation of the Nez Perce verb and on the semantic description of the verb and clause. Chapter 1 provides a grammar sketch. Chapter 2 discusses the morphology, syntax and semantics of verbal suffix complexes for tense, space, aspect and modality. Chapter 3 investigates the modal suffix o'qa, which is variously translated can, could (have), would (have), should, may, andmust, and used to make circumstantial, deontic and counterfactual claims. I argue that this suffix has only a non-epistemic possibility meaning, and that apparent necessity meanings are artifacts of translation. Chapter 4 investigates the future suffix u', generally translated will. Based on evidence from truth-value judgment tasks, conjunctions of u' sentences describing incompatible states of affairs, and negation, I argue that u' sentences have non- modal truth conditions. I also discuss challenges to this analysis from free choice licensing and from certain acceptable conjunctions of incompatible u' sentences. The second part of the dissertation explores the syntax of the verb and clause as revealed by the system of case-marking. Nez Perce case follows a tripartite pattern, with no case on intransitive subjects, and both ergative and objective cases in transitive clauses. Transitive clauses may alternatively surface with no case, however. I show that caseless transitive clauses in Nez Perce come in two syntactically and semantically distinguished varieties. In one variety, the subject binds a possessor phrase within the object. Chapter 6 takes up this construction together with possessor raising, which I analyze as involving movement to a [straight theta]-position. I argue that the absence of case under possessor-binding reflects an anaphor agreement effect. In the other variety of caseless clause, the object is a weak indefinite. Chapter 7 concludes that such objects are not full DPs. In chapter 8, I propose a morphological theory of case-marking which captures the cased/caseless distinction for transitive clauses. Both ergative and objective cases are analyzed as morphological results of the syntactic system of agreement.