The first toxicological reference values (TRVs) were introduced in the 1950s, along with the concept of acceptable daily intake. There are two types of TRVs: those established for dose-threshold effects and those for non-threshold effects. They are derived in two steps based on dose-effect and dose-response relationships: determining the critical dose and extrapolating into the low-risk range. For dose-threshold effects, extrapolation involves applying uncertainty factors with values ranging from 1 to 10; for effects without a dose threshold, the extrapolation is based on a model that assumes, by default, linearity in the lowermost part of the dose-response curve. Many organizations provide VTRs in databases accessible online. France has recently begun developing its own VTRs.