Upstalsboom

thumb|upright=1.5|The Upstalsboom by , 1921 During the Frisian freedom period, the Upstalsboom ( or ), also known as the Opstalsbam, was an assembly for emissaries of the Seven Sealands of medieval Frisia, located just outside the East Frisian town of Aurich () in modern-day Germany. The origins of the Upstalsboom, including its name, are unclear, but as far back as the 8th century the meeting place was used as a burial ground for the members of important Frisian families.

Attested in writing as early as the first half of the 13th century, the assembly convened every year on the Tuesday after Pentecost to discuss issues pertinent to all Frisian lands. Although marked by weak central authority and regular infighting, Frisian territories showed great success repelling foreign invaders. In 1323, the Statutes of Upstalsboom were ratified, providing a legal framework for interaction between the Seven Sealands, such as prohibiting certain actions, prescribing punishments for crimes, establishing exchange rates for currencies, providing legal rights between citizens of different sealands, and establishing a defense pact. The punishments described in the 1323 ratification are considered to have been extreme for the time and place, but when the treaty was reaffirmed in 1361, additional punishments were scaled back. Different versions of the statutes exist today, but it is one of the few legal texts with both Old Frisian and Latin translations still in existence.