This book constitutes the refereed proceedings of the 19th International Conference on Ad-Hoc, Mobile, and Wireless Networks, ADHOC-NOW 2020, held in Bari, Italy, in October 2020.*The 19 full and 4 short papers presented were carefully reviewed and selected from 39 submissions. The papers provide an in-depth and stimulating view on the new frontiers in the field of mobile, ad hoc and wireless computing. They are organized in the following topical sections: intelligent, programmable and delay- and disruption- tolerant networks; internet of drones and smart mobility; internet of things and internet of medical things; secure communication protocols and architectures; and wireless systems. *The conference was held virtually due to the COVID-19 pandemic.