CLAWAR 2018 is the twenty-first edition of International Conference series on Climbing and Walking Robots and the Support Technologies for Mobile Machines. The conference is organized by CLAWAR Association in collaboration with the Universidad Tecnológica de Panamá (UTP) within the premises of UTP, Panama City, Panama during 10 – 12 September 2018.CLAWAR 2018 brings new developments and associated new research findings in robotics technologies for shaping the future. The topics covered include assistive robotics for levels of augmentation to full support for elderly and disabled mobility, rehabilitation and function restoration; services to humans in industrial, public and domestic environments; new locomotion and design strategies to help in climbing on various terrains; navigation and localisation approaches, non-destructive testing and inspection strategies for industrial applications.The CLAWAR 2018 conference includes a total of 53 articles, including three plenary lectures, from 17 countries. This number has been arrived at through rigorous review of initial submissions, where each paper initially submitted has received on average three reviews.The editors would like to thank members of the International Scientific Committee and National Organising Committee for their efforts in reviewing the submitted articles, and the authors in addressing the comments and suggestions of the reviewers in their final submissions. It is believed that the CLAWAR 2018 proceedings will be a valuable source of reference for research and development in the rapidly growing area of mobile service robotics.