Since 1993 the International Workshop on Methods for the Development and Evaluation of Maritime Technologies (DEMaT) is an established series of scientific conventions in the field of fisheries and marine aquaculture research. On a biennial schedule international scientists from various fields of expertise share and discuss results of their multi-disciplinary investigations and developments. Ranging from research of fish biology and behaviour via improvements of fishing technologies to experimental as well as theoretical investigations of fishing gear and aquaculture installations, a wide variety of aspects is covered in this Workshop. The focus of the 12th International Workshop on Methods for the Development and Evaluation of Maritime Technologies (DEMaT'15), held in Aberdeen in October 2015, is on hydrodynamic loads as well as mathematical modelling and numerical simulation of netlike structures and related marine systems. Furthermore studies on fishing gear - sea bed interaction as well as design, construction, and optimisation of fishing gears and net cages along with methods and results in fishing research are presented.