Abstract: Manifolds equipped with torus actions are a central object of study in geometry and topology. In this talk, I will discuss the topological structure of smooth manifolds with free torus actions, focusing on the opological classification of closed, simply connected manifolds with a free cohomogeneity-four torus action. As an application, one may construct infinitely many manifolds with Riemannian metrics of positive Ricci curvature and isometric torus actions. This is joint work with Philipp Reiser.