The majority of known hadrons in the low-energy QCD spectrum are
resonances observed in multi-particle scattering
processes. First-principles determinations of the properties of these
unstable hadrons are a crucial goal in lattice QCD
calculations. Significant progress has been made in developing,
implementing and applying theoretical tools that connect finite-volume
lattice QCD quantities to scattering amplitudes, enabling
determination of masses and widths of various hadronic resonances. In
this talk, I will discuss recent advances in lattice QCD studies of
meson-baryon resonances, including the Lambda(1405) resonances, as
well as three-hadron resonances such as the doubly-charmed tetraquark.