This book contains the refereed proceedings of the Fourth Annual Mediterranean Ad Hoc Networking Workshop, Med-Hoc-Net 2005. Med-Hoc-Net 2005 consolidated the success of the previous editions of the workshop series. It aimed to serve as a platform for researchers from academia, research, laboratories, and industry from all over the world to share their ideas, views, reults, and experiences in the field of ad-hoc networking.