These proceedings bring together 63 papers from the 4th International Conference on Materials and Applications for Sensors and Transducers (MAST), held in June 2014 in Bilbao, Spain. They emphasize sensors manufactured by low-cost methods, such as hybrid sensors and smart specialization devices, and include micro-nano technology from different kinds of solid-state, liquid, and gaseous materials, and transducer applications and their design, development, and use of sensing data. Contributors work in physics, engineering, chemistry, and other fields in countries across the globe. Annotation ©2015 Ringgold, Inc., Portland, OR (protoview.com)