This study investigates in the context of the Euronext, whether joining an exchange group affects herding in the group’s member-markets and if this effect persists when accounting for various domestic and international market states, the dynamics of the group’s member-markets and the outbreak of financial crises. We find that herding is significant post-merger in all four constituent equity markets (Belgium, France, the Netherlands and Portugal) of the Euronext, with herding in Portugal being significant (yet less strong) pre-merger as well. These results are robust when controlling for various domestic and international market states, as well as the dynamics of the group’s markets. The period following the outbreak of the euro-zone soverei...