The theory of statistical-mechanical lattice-gas modeling of adsorption is reviewed and shown to be applicable to a range of electrochemical problems dominated by effective, lateral adsorbate-adsorbate interactions. A general strategy for applying the method to specific systems is outlined, which includes microscopic model formulation, calculation of zero-temperature phase diagrams, numerical calculation of thermodynamic and structural quantities at non-zero temperatures, and estimation of effective, lateral interaction energies that cannot be obtained by first-principles methods. Phenomena that are discussed include poisoning and enhanced adsorption, and illustrative applications to specific systems are reviewed. Particular problems considered are : the poisoning by sulfur of hydrogen adsorption on platinum(lll), the electrochemical adsorption of naphthalene on polycrystalline copper and of urea on single-crystal platinum(100), and the underpotential deposition of copper cn single-crystal gold(lll).