In the literature, most of the authors agree that addressing "grand challenges" implies systems transformation and requires social, economic and technological changes. It involves new policy rationales and design and consequently new approaches of research impact assessment (RIA). The challenge is to develop methods able to improve our understanding of the impact generating mechanisms, to assess a broader set of impacts, and to incorporate a mix of complementary approaches (combining qualitative and quantitative evaluation, achieving a multi-objective evaluation, and evaluating impacts at various level of aggregation). The six papers in this Special Issue present, discuss and even assess a new generation of RIA approaches. None of the papers covers all the RIA challenges highlighted above. At this stage, it would be illusive to develop a common evaluation approach, with standardized methods and metrics. We contend that the availability of a diversity of tools is a precious asset if impact assessment allows a conscientious attention to the transformative effects of research.