Abstract
Velicko [1968] introduced the concepts of theta - closure and theta - interior operations. The collection of all theta - open sets in a topological space X forms a topology on X. In this paper we introduce theta - irresolute, theta - closed, pre - theta - open, and pre - theta - closed mappings and investigate properties and characterizations of these new types of mappings. We also explore further properties of the well-known notions of theta - continuous and theta- open mappings.