This lecture introduces Darcy's Law, an empirical equation formulated by Henry Darcy in the 19th century, which describes the flow of fluids through porous media. The law states that the flow rate (Q) is directly proportional to the cross-sectional area (A) and the hydraulic gradient (hL/l), and inversely proportional to the length (l) of the medium. The hydraulic conductivity (K), a constant dependent on the medium's permeability and the fluid's properties, also plays a crucial role. Variations in the medium's coarseness and the fluid's viscosity affect the flow rate, with coarser media allowing greater flow and higher specific yields. Therefore, Darcy's Law provides a foundational understanding of fluid movement in groundwater hydrology and other applications involving porous materials.