The Threshold of Toxicological Concern (TTC) and the Threshold of Regulation (TOR) are risk assessment tools assigning human exposure thresholds to substances with known chemical structure, but unknown toxicity. With improving analytical techniques an increasing number of previously unsuspected substances is discovered in food and food contact materials. These chemicals include unwanted reaction products, impurities, metabolites and/or breakdown products. However, the application of the TTC in the risk assessment of food contact materials remains debated. In a new report, the Food Packaging Forum (FPF) reviews advantages and challenges of threshold concepts.