This book is a research monograph on high-Frequency Seafloor Acoustics. It will provide a critical evaluation of the data and models pertaining to high-frequency acoustic interaction with the seafloor, which will be of interest to researchers in underwater acoustics and to developers of commercial and military sonars. Models and data are presented so as to be readily usable, backed up by extensive explanation. Much of the data is new, and the discussion in on two levels: concise descriptions in the main text backed up by extensive technical appendices. This monograph will provide ready access to data and current models and a clear path through a somewhat confusing literature. There is an extensive bibliography, and the main text points towards the essential literature.