The Euromix project has developed new models and strategies to identify groups of chemicals to consider in a risk assessment. One of the aims is to develop practical tools that can be applied to large groups and to quantify uncertainties. Tiered approaches have been developed that include the uncertainty of Cumulative Assessment Group membership and uncertainties due to missing hazard and exposure data that arise for large groups. This deliverable report describes the approach as implemented in the MCRA software and gives examples.