2-Butenal (also known as crotonaldehyde) is an a, ss-unsaturated aldehyde and consequently a very reactive compound. It is a chemical intermediate used chiefly in the manufacture of sorbates, solvents, and, to a lesser extent, pharmaceutical products and aroma chemicals. This document studies the pharmacokinetics, environmental exposure, chemical toxicology and carcinogenicity of 2-butenal. However, to enable an understanding and evaluation of this aldehyde in the context of environmental health, other aldehydes, such as formaldehyde, acetaldehyde, and acrolein, are mentioned for comparison, where necessary, in the relevant sections.