  Feshbach resonances are the essential tool to control the interaction between
atoms in ultracold quantum gases. They have found numerous experimental
applications, opening up the way to important breakthroughs. This Review
broadly covers the phenomenon of Feshbach resonances in ultracold gases and
their main applications. This includes the theoretical background and models
for the description of Feshbach resonances, the experimental methods to find
and characterize the resonances, a discussion of the main properties of
resonances in various atomic species and mixed atomic species systems, and an
overview of key experiments with atomic Bose-Einstein condensates, degenerate
Fermi gases, and ultracold molecules.
