The Poincaré Seminar is held twice a year at the Institut Henri Poincaré in Paris. The goal of this seminar is to provide up-to-date information about general topics of great interest in physics. Both the theoretical and experimental results are covered, with some historical background. Particular care is devoted to the pedagogical nature of the presentation. This volume is devoted to the quantum Hall effect. After a historical and general presentation by Nobel prize winner Klaus von Klitzing, discoverer of this effect, the volume proceeds with reviews on the mathematics and physics of both the integer and fractional case. It includes up to date presentations of the tunneling and metrology experiments related to the quantum Hall effect. It will serve the community of physicists and mathematicians at professional or graduate student level.