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In the early sixties, we c haracterized congruence lattices of universal algebras as algebraic lattices; then our interest turned to the characterization of congruence lattices of lattices. Since these lattices are distributive, we gured that this must be an easier job. After more then 35 years, we know that we w ere wrong.In this Appendix, we give a brief overview of the results and methods. In Section 1, we deal with nite distributive lattices; their representation as congruence lattices raises many i n teresting questions and needs specialized techniques. In Section 2, we discuss the general case.A related topic is the lattice of complete congruences of a complete lattice. In contrast to the previous problem, we can characterize complete congruence lattices, as outlined in Section 3.