This is a survey on the infinite group problem, an infinite-dimensional relaxation
of integer linear optimization problems introduced by Ralph Gomory and Ellis Johnson in
their groundbreaking papers titled "Some continuous functions related to corner polyhedra
I, II" [Math. Programming 3 (1972), 23-85, 359-389]. The survey presents the infinite group
problem in the modern context of cut generating functions. It focuses on the recent
developments, such as algorithms for testing extremality and breakthroughs for the k-row
problem for general k >= 1 that extend previous work on the single-row and two-row
problems. The survey also includes some previously unpublished results; among other things,
it unveils piecewise linear extreme functions with more than four different slopes. An
interactive companion program, implemented in the open-source computer algebra package
Sage, provides an updated compendium of known extreme functions.