Lattice QCD calculations of hadron spectroscopy

This chapter provides a pedagogical introduction to theoretical studies of hadrons based on the fundamental theory of strong interactions - Quantum ChromoDynamics. A perturbative expansion in the strong coupling is not applicable at hadronic energy scales. Lattice Quantum Chromodynamics is the formulation of the fundamental theory on a discrete space-time grid, which enables first-principles, systematically improvable, numerical simulations of strong interaction physics. This chapter explains how the masses of strongly stable and strongly decaying hadrons are determined. The strongly decaying hadrons have to be inferred from the corresponding scattering processes. Therefore, one of the main aims is to describe how the scattering amplitudes are extracted from a lattice simulation. The examples of spectra, widths, and scattering amplitudes are shown for conventional as well as exotic hadrons.