Research on theoretical aspects of computing has a direct impact on the practice of computer systems development. Over many decades, fundamental theories have emerged to describe functionality, temporal behavior and resource consumption. Theories of application domains are beginning to be exploited for modelling and analyzing intended computing systems before the expensive commitment is made to real programs and hardware. Recent years have seen major improvements in the cost-effectiveness of tools supporting the exploitation of theories through proof, model-checking and testing. Against this encouraging background, we are pleased to present papers that show something of the liveliness and diversity of research in theoretical aspects of computing today.