Volume II/20 provides critically evaluated data on free molecules, obtained from infrared spectroscopy and related experimental and theoretical investigations. The volume is divided into four subvolumes, A: Diatomic Molecules, B: Linear Triatomic Molecules, C: Nonlinear Triatomic Molecules, D: Polyatomic Molecules. The present subvolume II/20 B3 deals with the linear triatomic nitrous oxide molecule, N2O (NNO). Both the normal isotopic species 14N14N16O and eleven of its isotopic varieties have been considered in this subvolume. The tables are preceded by an additional index to help the search for specific information. Subvolume B3 contains a CD-ROM. Further subvolumes are in preparation.