This book constitutes the refereed proceedings of the 14th International Workshop of Descriptional Complexity of Formal Systems 2012, held in Braga, Portugal, in July 2012. The 20 revised full papers presented together with 4 invited papers were carefully reviewed and selected from 33 submissions. The topics covered are automata, grammars, languages and related systems, various measures and modes of operations (e.g., determinism and nondeterminism); trade-offs between computational models and/or operations; succinctness of description of (finite) objects; state explosion-like phenomena;...