2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/150704In this article we review a recent calculation of the two-loop $σ$-model corrections to the T-duality map in string theory. Using the effective action approach, and focusing on backgrounds with a single Abelian isometry, we give the $O(α')$ modifications of the lowest-order duality transformations. The torsion plays an important role in the theory to $O(α')$, because of the Chern-Simons couplings to the gauge fields that arise via dimensional reduction.9 pages, Latex, no figures. Based on the talks given by N. Kaloper at the conferences Black Holes: Theory and Mathematical Aspects at Banff, AB, Canada and the $7^{th}~C^2GR^2A$ in Calgary, AB, Canada, May 31 - June 7, 1997High Energy Physics - Theorytext