Mechanical Molecular Models -- Molecular mechanics Capillary phenomena The internal energy of a liquid The continuous surface profile The mean molecular field Thermodynamics -- Thermodynamics and kinetic theory The thermodynamics of the surface Surface functions The spherical surface Quasi-thermodynamics -- a first look The Theory of van der Waals -- The surface tension Independently variable densities Gibbs adsorption equation in the van der Waals theory Constraints on the range of fluctuations Statistical Mechanics of the Liquid-Gas Surface -- Distribution and correlation functions The pressure tensor The virial route to the surface tension Functionals of the distribution functions The surface tension from the direct correlation function Equivalence of the two expressions for the surface tension The spherical surface Density fluctuations and their correlation Local thermodynamic functions Model Fluids in the Mean-Field Approximation -- Introduction: mean-field theory of a homogeneous fluid of attracting hard spheres Liquid-gas interface in the model of attracting hard spheres Lattice-gas model: one component Lattice-gas model: two components Penetrable-sphere model: theory Penetrable-sphere model: applications Penetrable-sphere model: spherical surfaces Computer Simulation of the Liquid-Gas Surface -- The experimental background The methods of computer simulation The density profile The surface tension Further work Calculation of the Density Profile -- Solution of the YBG equation Approximations for the direct correlation function Modified van der Waals theories Perturbation theories Surface tension Three-Phase Equilibrium -- Contact angles and Neumann's triangle Spreading and Antonow's rule The [alpha gamma] interface Phase transitions in interfaces. The Cahn transition Three-phase line and line tension Interfaces Near Critical Points -- Introduction: mean-field approximation Digression on the Ornstein-Zernike theory of the pair-correlation function Digression on critical-point exponents Van der Waals theory with non-classical exponents Tricritical points Non-critical interface near a critical endpoint Renormalization-group theory; field-theoretical models Thermodynamics Dirac's delta-function