The XI Black Holes Workshop will take place at IST-Lisbon on 17-18 December 2018. The Black Holes Workshops gather researchers working on physical and mathematical problems of black holes, both in its classical and quantum aspects, as well as their connections to general relativity and gravitation, string theory, cosmology, and astrophysics, and stimulate the interaction between all these issues. The eleventh edition of the Black Holes Workshop celebrates the 50th anniversary of the name Black Hole.