Evidentialist Logic Matthew P. Wampler-Doty Abstract: The purpose of this thesis is to present a formal framework which tries to present a novel modal logic for reasoning about knowledge. Subsequently, we shall conform to the following structure: §1 First, we shall elaborate the on our philosophical intuition behind our epistemic logic, and provide a sketch of how the system will ultimately be formulated. §2 Next, we give formal details of the system we will develop. Single agent semantics for concrete models is developed and an elimination theorem is derived. The semantics are then extended to a multi-agent setting, and finally Kripke semantics as an abstraction on our previous concrete semantics. §3 Here we present several axiom systems for the abstract and concrete semantics. We show via our investigated completeness results that Kripke semantics faithfully abstracts away from our concrete semantics. We also derive the small model property for all of the axiom systems we provide, and discuss their inter-relationships in terms of a lattice of conservative extensions. Some complexity results are also provided. §4 Finally. we shall look at applications of the framework developed. We show that imposing certain popular axioms leads to collapse results for concrete EviL models and Kripke seman- tics. We then provide three embeddings of intuitionistic logic into EviL, and discuss some of their connections to the philosophical literature. §5 Finally, the framework developed shall be compared to other approaches.