A process for the preparation and/or purification of clavulanic acid or a pharmaceutically acceptable salt thereof comprises
i) contacting impure clavulanic acid or an alkali metal salt thereof in an organic solvent, with tertiary octylamine;
ii) isolating the tertiary-octylamine salt of clavulanic acid formed;
iii) converting the thus formed salt into clavulanic acid or a pharmaceutically acceptable salt or ester thereof.