  This is an expository paper about applications of ruled surface theory in
incidence geometry. It surveys the results that have been proven, gives an
overview of the methods, and discusses some open problems and further
directions. It will appear in the book Journey Through Discrete Mathematics, a
Tribute to Jiri Matousek, edited by Martin Loebl, Jaroslav Nesetril and Robin
Thomas, due to be published by Springer.
