his book constitutes the refereed proceedings of the 18th International Conference on Descriptional Complexity of Formal Systems, DCFS 2016, held in Bucharest, Romania, in July 2016. The 13 full papers presented together with 4 invited talks were carefully reviewed and selected from 21 submissions. Descriptional Complexity is a field in Computer Science that deals with the size of all kind of objects that occur in computational models, such as Turing Machines, finte automata, grammars, splicing systems and others. The topics of this conference are related to all aspects of descriptional complexity. .