This book constitutes the thoroughly refereed proceedings of the 12th International Conference on Evaluation of Novel Approaches to Software Engineering, ENASE 2017, held in Porto, Portugal, in April 2017.The 12 full papers presented were carefully reviewed and selected from 102 submissions. The mission of ENASE is to be a prime international forum to discuss and publish research findings and IT industry experiences with relation to the evaluation of novel approaches to software engineering. The conference acknowledges necessary changes in systems and software thinking due to contemporary shifts of computing paradigm to e-services, cloud computing, mobile connectivity, business processes, and societal participation.