International Axion Observatory (IAXO) is a new generation axion helioscope aiming to search for axions and axion-like particles with a sensitivity to the axion-photon coupling that is 1 to 1.5 orders of magnitude beyond the one achieved by currently the most sensitive axion helioscope, CAST. IAXO relies on large improvements in magnetic field volume, X-ray focusing optics and detector backgrounds with respect to CAST. Additional IAXO searches would include electron-coupled axions, relic axions, and other more generic axion-like particles.