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.Introduction.- Energy level designations.- Effective Hamiltonians. Energy matrix. Diagonal elements. Off-diagonal elements. Energy expressions referred to the ground state. Vibrational states. Rotational states. Conversion table for energy-related units and selected fundamental constants. Formulas for determining rotational constants.- Effective parameters. Band center and band origin. Comments on BHO (HBO) (see Chap.6 of subvolume II/20B1). Diagonalizing the energy matrix. Effective molecular parameters. Unperturbed vibrational states. Effects of perturbations. Quadrupole coupling. Potential energy function (PEF).- PEF expanded as a Taylor series. Curvilinear valence coordinates and Morse functions. Dimensionless normal coordinates. Specific forms of the PEF. Dipole moment.- General equations. Specifics related to COS (OCS) (see Chap.38 of subvolume II/20B1). Intensities.- Intensities of spectral lines. Integrated absorption intensities. Total internal partition sum. F-factors (Herman-Wallis factors). Intensity expressions. Intensity units and conversion table. Line profiles. Lorentz profile. Doppler profile. Voigt profile. Galatló6