Youssef Dey Mosque, or Sidi Youssef Mosque, is a historic Ottoman-era mosque located in the old city of Tunis in Tunisia. The mosque was founded as a small mosque in the year 1612 AD by Yusuf Dey (Youssef Dey,) the Dey of Tunis during the Ottoman era, who then opened it as an Friday mosque in the year 1631. The mosque, which includes the mausoleum of Youssef Dey, was restored in the 19th century and then inscribed as a UNESCO World Heritage Site in 1979 as part of Medina of Tunis.