Advanced composite materials engineering is one of the most important area of research and development at the present time. Composite materials are a mixture of two or more different components, whose properties complement each other, and the result is a material with superior properties to those specific to each component. The utilization of composite materials is growing fast in strategic fields such as the aircraft, automotive, biomedical, naval and space industries, as well as in textile, paints, magnetic fluids, high-quality paper coatings, and microelectronics. These Proceedings of the 4th International Conference "Advanced Composite Materials Engineering" COMAT 2012 include 67 papers, which analyse many important practical applications. The topics range from wood engineering, sonic composite visualization, asphalt mixtures with polypropylene fibers and dental filling materials, to design optimization of composite stiffened structures for aerospace applications, new lignocellulosic composite materials, incorporation of different inorganic nanoparticles in polymer matrix, and carbon fiber reinforced polymer-matrix composites.