Many of the materials around us are polycrystalline materials composed of many crystals or "grains". Grain boundaries are interfaces between two grains of different orientations, and their structures and properties depend on the crystal orientation relationship between the neighbouring grains. The properties of grain boundaries often control the physical properties of the entire polycrystalline material. One example of the importance of grain boundaries is the issue in solar cells of polycrystalline materials, a key technology in the search for greener and sustainable energy, grain boundaries are one of the main causes of losses causing decreases in the conversion efficiency of sunlight to electrical energy, but an important point is that not all grain boundaries contribute to this loss to the same extent. There are certain types at which the decrease in the conversion efficiency hardly occurs at all. This example shows that it is important to make the best use of the individual characteristics of grain boundaries to design and control materials properties. The research in our group takes as its basis grain boundary and interface science and engineering and the PMP triangle of 'Microstructure-Properties-Processing', with the aim of developing advanced materials with excellent function and performance.