This survey paper collects some of older and quite new concepts and results from descriptive set topology applied to study certain infinite-dimensional topological vector spaces appearing in Functional Analysis,
including Fréchet spaces, (L F)-spaces, and their duals, (D F)-spaces and spaces of continuous real-valued functions C(X ) on a completely regular Hausdorff space X . Especially (L F)-spaces and their duals arise in many fields of Functional Analysis and its applications, for example in Distributions Theory, DifferentialEquations and Complex Analysis. The concept of a realcompact topological space, although originally introduced and studied in General Topology, has been also studied because of very concrete applications in Linear Functional Analysis.