Non-Riemannian Geometry deals basically with manifolds dominated by the geometry of paths developed by the author, Luther Pfahler Eisenhart, and Oswald Veblen, who were faculty colleagues at Princeton University during the early twentieth century. Eisenhart played an active role in developing Princeton's preeminence among the world's centers for mathematical study, and he is equally renowned for his achievements as a researcher and an educator. In Riemannian geometry, parallelism is determined geometrically by this property: along a geodesic, vectors are parallel if they make the same angle with the tangents. In non-Riemannian geometry, the Levi-Civita parallelism imposed a priori is replaced by a determination by arbitrary functions (affine connections). In this volume, Eisenhart investigates the main consequences of the deviation. Starting with a consideration of asymmetric connections, the author proceeds to a contrasting survey of symmetric connections. Discussions of the projective geometry of paths follow, and the final chapter explores the geometry of sub-spaces.