article published yes Uli Wagner author 36690CA2-F248-11E8-B48F-1D18A9856A870000-0002-1494-0568 UlWa department Expander graphs (sparse but highly connected graphs) have, since their inception, been the source of deep links between Mathematics and Computer Science as well as applications to other areas. In recent years, a fascinating theory of high-dimensional expanders has begun to emerge, which is still in a formative stage but has nonetheless already lead to a number of striking results. Unlike for graphs, in higher dimensions there is a rich array of non-equivalent notions of expansion (coboundary expansion, cosystolic expansion, topological expansion, spectral expansion, etc.), with differents strengths and applications. In this talk, we will survey this landscape of high-dimensional expansion, with a focus on two main results. First, we will present Gromov’s Topological Overlap Theorem, which asserts that coboundary expansion (a quantitative version of vanishing mod 2 cohomology) implies topological expansion (roughly, the property that for every map from a simplicial complex to a manifold of the same dimension, the images of a positive fraction of the simplices have a point in common). Second, we will outline a construction of bounded degree 2-dimensional topological expanders, due to Kaufman, Kazhdan, and Lubotzky. Societe Mathematique de France2022 eng 0037-9484 2102-622X 00095836440000710.24033/ast.1188 438281-294 Wagner, Uli. “High-Dimensional Expanders (after Gromov, Kaufman, Kazhdan, Lubotzky, and Others).” <i>Bulletin de La Societe Mathematique de France</i>. Societe Mathematique de France, 2022. <a href="https://doi.org/10.24033/ast.1188">https://doi.org/10.24033/ast.1188</a>. U. Wagner, “High-dimensional expanders (after Gromov, Kaufman, Kazhdan, Lubotzky, and others),” <i>Bulletin de la Societe Mathematique de France</i>, vol. 438. Societe Mathematique de France, pp. 281–294, 2022. Wagner U. 2022. High-dimensional expanders (after Gromov, Kaufman, Kazhdan, Lubotzky, and others). Bulletin de la Societe Mathematique de France. 438, 281–294. Wagner, U. (2022). High-dimensional expanders (after Gromov, Kaufman, Kazhdan, Lubotzky, and others). <i>Bulletin de La Societe Mathematique de France</i>. Societe Mathematique de France. <a href="https://doi.org/10.24033/ast.1188">https://doi.org/10.24033/ast.1188</a> U. Wagner, Bulletin de La Societe Mathematique de France 438 (2022) 281–294. Wagner U. High-dimensional expanders (after Gromov, Kaufman, Kazhdan, Lubotzky, and others). <i>Bulletin de la Societe Mathematique de France</i>. 2022;438:281-294. doi:<a href="https://doi.org/10.24033/ast.1188">10.24033/ast.1188</a> Wagner, Uli. “High-Dimensional Expanders (after Gromov, Kaufman, Kazhdan, Lubotzky, and Others).” <i>Bulletin de La Societe Mathematique de France</i>, vol. 438, Societe Mathematique de France, 2022, pp. 281–94, doi:<a href="https://doi.org/10.24033/ast.1188">10.24033/ast.1188</a>. 143812023-10-01T22:01:14Z2025-09-10T09:55:10Z