In many application domains, such as automotive, avionics, telecommunications, process control or multimedia, software components must fulfill timing constraints. In such real-time systems, the timely delivery of results is as important as their correctness. Guaranteeing that tasks can meet their deadlines requires using specific design and analysis techniques that include task and message scheduling considering various kinds of supporting platforms, model-driven development, worst-case execution time estimation, design of time-predictable infrastructures, real-time-specific compilers, programming languages, middleware and operating systems. These topics are at the heart of several annual international conferences that gather researchers from all around the world. The real-time and network systems conference (RTNS) is one of them. This special issue focuses on the optimization of real-time systems. It includes extended versions of three selected papers that have been presented at the 20th RTNS held in Pont-à-Mousson, France, in November 2012. Each paper includes significant extra material and has been peer-reviewed to meet the quality standard required by the journal.