We use neutron reflectometry to study a variety of fundamental physical and chemical phenomena at solid-solid, liquid-liquid, solid-liquid, and solid- or liquid-gas interfaces. By measuring the specular reflectivity as a function of glancing angle, we can determine both chemical and magnetic density profiles normal to the surface. We can also measure nonspecular scattering, from which we can derive in-plane information. Systems of interest include polymer films, magnetic thin films and multilayered structures (using polarized beams), superconducting films (magnetic penetration depth measurements), lipid bilayers, Langmuir-Blodgett films, metal hydride films, and electrochemical surfaces (in situ studies in active cells).