This book constitutes the refereed post-conference proceedings from the 18th EAI International Conference on Body Area Networks, BODYNETS 2024-A, held in Milan, Italy, in February 5-6, 2024. The 20 full papers presented here were carefully reviewed and selected from 48 submissions. These papers have been organized in the following topical sections: Implantable devices and In-body communication; Body area networks and transmission technologies; Smart healthcare applications; Privacy and security in wireless body area networks.