Computing systems are rapidly evolving into heterogeneous machines featuring many processor cores. This leads to a tremendous complexity with an unprecedented number of available design and optimization choices for architectures, applications, compilers and run-time systems. Using outdated, non-adaptive technology results in an enormous waste of expensive computing resources and energy, while slowing down time to market. The 3rd International Workshop on Adaptive Self-tuning Computing Systems is an interdisciplinary forum for researchers, practitioners, developers and application writers to discuss ideas, experience, methodology, applications, practical techniques and tools to improve or change current and future computing systems using self-tuning technology. Such systems should be able to automatically adjust their behavior to multi-objective usage scenarios at all levels (hardware and software) based on empirical, dynamic, iterative, statistical, collective, bio-inspired, machine learning and alternative techniques while fully utilizing available resources. All papers will be peer-reviewed including short position papers and should include ideas on how to simplify, automate and standardize the design, programming, optimization and adaptation of large-scale computing systems for multiple objectives to improve performance, power consumption, utilization, reliability and scalability.