Arrondo Esteban, Enrique2023-06-202023-06-202002-091424-928610.1007/s00032-002-0008-4https://hdl.handle.net/20.500.14352/57036A line congruence is an irreducible subvariety of dimension n−1 in the Grassmannian of lines in Pn. There are two numerical invariants associated to a line congruence: the order, which is the number of lines passing through a general point of Pn, and the class, which is the number of lines of the congruence contained in a general hyperplaneH and meeting a general line inH. The paper reviews the classification of line congruences of order 0 and 1, and then gives some new results online congruences of order 2 in P3, which is a work in progress. The last section states some open questions.engjournal articlehttp://www.springerlink.com/content/1424-9286/open access512GrassmanniansSchubert varietiesÁlgebra1201 Álgebra