Jacob (or Jaak, or Jacques) van Thienen (also called van Gobertingen) was a Flemish architect of the early 15th century (the dates of his birth and death are unknown). He is believed to have designed the spectacular Brussels Town Hall (Hôtel de Ville) circa 1402. This Gothic building, which stands in the city's Grand Place, is widely regarded as a masterpiece of medieval European secular architecture. The building's distinctive belfry was, however, the work of a different architect, Jan van Ruysbroeck.
Van Thienen may also have built the southern aisle of the Saint Michael and Saint Gudula Cathedral in Brussels, around 1400.