When he was appointed Professor of Theoretical Mechanics, back in 1966, Professor Anthony James Merrill Spencer [1] (Elected FRS in 1987) delivered an inaugural lecture, entitled ''Mechanics, Mathematics and Materials.'' Despite the substantial progress that continuum mechanics has enjoyed since that time, the lecture remains surprisingly contemporary. Its contents continue to resonate today to the extent that its reading leaves the strong impression that if published in the open literature, the lecture might be both revealing and inspirational to yet another generation of researchers. These impulses led me to make a request and obtain publication permission from both Tony Spencer's family and the George Green Library of the University of Nottingham.I next approached a small number of colleagues and proposed them to compose a relevant research article that could accompany and support the lecture's publication. The proposed enterprise was embraced with overwhelming support. It was destined to escalate into a relevant journal special issue that was naturally directed toward and finally associated with the journal ''Mathematics and Mechanics of Solids'' (MMS).Formal submission invitations were sent out at the very beginning of August 2021, after a proper consultation with potential contributors settled an indicative submission deadline in the middle of March 2022. The received contributions went through the standard review process of this journal and the whole process progressed smoothly. I thankfully express my sincere gratitude and appreciation to every author and every anonymous reviewer involved in the composition of this volume, as well as to the MMS Editor in Chief, Professor David Steigmann, for his sterling work, support, and pleasant editorial collaboration. Special thanks are also due to Mr Milad Shirani, Department of Mechanical Engineering, University of California at Berkeley, for the substantial technical assistance he offered in the pre-publication preparation of Professor Spencer's inaugural lecture.The lecture is naturally the leading article of this MMS special edition. It is followed by a comprehensive supporting article which, in brief, marks the significance that Professor Tony Spencer gave to Mathematics and its interaction with Continuum Mechanics, describes the state of the art at the time of the lecture, provides a fair account of the development that have followed since in both subjects, and acknowledges the marked successes of their interaction as well as the room that remains available for many more. Tony Spencer is remarkably one of the co-authors of the third article, while the fourth contribution contains a photograph of handwritten text, penciled by him more than half a century ago. Every single one of the eighteen remaining papers bears clear marks and signs of Professor Spencer's influential publications, and lifelong commitment and contribution to theoretical solid mechanics.A detailed list of Tony Spencer's publications needs not be presented here. This is available in the liter...