This special issue covers the main results of the European Sixth Framework Integrated Research project NoMiracle (Novel Methods for Risk Assessment of Cumulative stressors in Europe). New tools to analyse, characterise and quantify the combined risks to health or the environment from multiple stressors are presented or reviewed. Examples of cumulative stressors are mixtures of chemicals alone or in combination with biological or physical environmental factors such as pathogens and climate extremes. Among the main findings, the scientific work points at the importance of time in dealing with toxicity, and in particular the toxicity of chemical mixtures, the natures of the uncertainties associated with risk assessment and the value of visualisation in identifying and quantifying the most relevant risks. A major conclusion of the project is that researchers and regulators should focus on the receptor rather than on the single stressor or combination of agents. There is also a need for more efforts on mechanistic understanding and for a mechanism-based framework for interpreting mixture/multiple stressor effects.The new tools are available on the internet (http://nomiracle.jrc.ec.europa.eu).