I will briefly review an interesting and poorly understood correspondence between 4-dimensional heterotic theories compactified on Calabi-Yau threefolds. Though not yet a proven string “duality” this correspondence arises in (0,2) Gauged Linear Sigma Models (GLSMs) under the name of “target space duality”. I will review recent developments in Target Space Duality within heterotic theories and discuss some of their possible consequences for F-theory.