The dissertation deals with certain electrodynamic properties of type-II superconductors which are derived from phenomenological theory. For both discrete and continuous type-II superconductors, vortex dynamics are investigated and their consequences described. Many of the results of the thesis are expected to apply to high-transition temperature superconductors. The subject of dimensional crossover in a layered anisotropic superconductor and its implications for vortex structure is discussed. For discrete superconductors, specific quantitative results include the viscous drag coefficient for vortex motion parallel to the layers of a Josephson-coupled layer model, the lower critical field for parallel applied field for such a model, and a vortex inertial mass for motion parallel to the layers;A self-consistent approach for describing the various fields and densities associated with a vortex lattice in a continuous superconductor subject to small-amplitude driving forces is developed. This approach takes into account the nonlocality of vortex interactions, yielding a complex penetration depth which in turn gives certain linear response functions such as the complex permeability. The resulting theory is expected to be valid over a wide range of magnetic inductions, temperatures, and frequencies. The frequency- and temperature-dependent vortex mobility is developed, providing a unifying tool for describing vortex dynamics. By including a random force in the vortex equation of motion and treating it in analogy to Brownian motion, the vortex mobility is extended to include flux creep effects. For continuous superconductors, specific quantitative results are given for the vortex inertial mass and dynamic mobility and complex rf surface impedance and permeability. A description of energy dissipation and screening is given in terms of the rf surface impedance and permeability.