This book presents an experimental study on wave reflection on coastal structures and current state of the art anti-reflective designs of breakwaters. In particular, this book shows the results from an experimental study on a new low-reflectivity quay wall caisson based on the MUCAR patent. The original idea of a multi-cell circuit scheme consisting of connecting caisson cells in two different directions to create circuits of appropriate length to optimize the given response to low-frequency incident waves was considered. Results from twelve 1/35 scale physical model tests, carried out at the Ports and Coasts Laboratory of the Polytechnic of Valencia, show the relationship observed between experimental coefficients of reflection (CR) and the structural and wave conditions for a variety of Mediterranean and Atlantic sea conditions. Experimental findings confirm that the new low-reflectivity quay wall caisson can be designed to be especially efficient for a given spectral bandwidth, including very-low-frequency waves.