  It is often assumed that few- and many-body systems can be accurately
described by considering only pairwise two-body interactions of the
constituents. We illustrate that three- and higher-body forces enter naturally
in effective field theories and are especially prominent in strongly
interacting quantum systems. We focus on three-body forces and discuss examples
from atomic and nuclear physics. In particular, we highlight the importance and
the challenges of three-nucleon forces for nuclear structure and reactions,
including applications to astrophysics and fundamental symmetries.
