Everyday life and critical aspects of our economy, defense, and government depend on software, and software, in turn, depends on high-level programming languages and their efficient implementations. Ever since Fortran and its automatic compiler in the late 50s, language implementation techniques have been central to computer science, and have relied on well-defined theoretical contributions and central principles. The focus of this summer school is the mix or interplay of theory and practice in language implementation mechanisms, such as compilers or run-time systems. The main aim of this summer school is to enable participants to conduct research in the area, thereby contributing to improved software.