This book constitutes the refereed proceedings of the 18th International Conference on Ad-Hoc, Mobile, and Wireless Networks, ADHOC-NOW 2019, held in Luxembourg, in October 2019. The 37 full and 10 short papers presented were carefully reviewed and selected from 64 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: IoT for emergency and disaster management; scheduling and synchronization in WSN; routing strategies for WSN; LPWANs and their integration with satellite; performance improvement of wireless and sensor networks; optimization schemes for increasing sensors lifetime; vehicular and UAV networks; body area networks, IoT security and standardization.