This book constitutes the proceedings of the 18th International System Design Language Forum,  SDL 2017, held in Budapest, Hungary, in October 2017. The 10 full papers presented in this volume were carefully reviewed and selected from 17 submissions. The selected papers cover a wide spectrum of topics related to system design languages ranging from the system design language usage to UML and GRL models; model-driven engineering of database queries; network service design and regression testing; and modeling for Internet of Things (IoT) data processing.