  The aim of the hadron physics research programs conducted at J-PARC is to
explore the structure of hadronic matter using the world's highest-intensity
meson beams. Since the first beam was extracted at the hadron experimental
facility (HEF) in February 2009, a wide variety of physics experiments have
been proposed and performed to address open questions regarding quantum
chromodynamics (QCD) at low energy. The high-intensity $K^-$ and high-momentum
beams available at J-PARC open a new era in hadron and nuclear physics, in
which strange and charm quarks play an important role. We review the programs
focused on addressing the hadron structure as strongly interacting composite
particles, the origin of hadron mass, and interactions between hadrons under
broken flavor SU(3) symmetry.
