​​For centuries Gernika has been the venue for assemblies of representatives of the towns and villages of Bizkaia.

The earliest records of their meetings beneath the now famous oak tree date from the 14th century. These assemblies sought to establish a set of laws and a system of representation of the people. The Assembly House and the Tree of Gernika are therefore must-see attractions, as they are living symbols of the history of the Basque people.

The Assembly House stands beside the great oak where in olden days the kings of Castile swore to uphold Basque laws and privileges. It is a meeting point for all the territories of the Basque Country, which share the same cultural and ethnographic traditions, extending beyond political frontiers.Nowadays it acts as the venue for such important ceremonies as the swearing in of the Premier of the Basque Government and the leader of the provincial council.​