The lecture on groundwater hydrology introduces the terminology, principles, processes and applications of groundwater hydrology. Groundwater recharge (direct through soils and indirect from rivers and surface water) is described and presented for different climates and environments. Different types of aquifers (phreatic and confined), their properties and parameters are introduced. Methods for the measurement of groundwater systems and for the evaluation of data are presented. Pumping test analysis, slug tests, simple injection/draw-down tests and their application are described. Special emphasis will be on the relevance of groundwater for hydrological systems, e.g. runoff generation (groundwater ridging), variable discharge zones, catchment response, spring-flow dynamics, and on the interaction of surface and groundwater hydrology. In the course analytical 3D models will be used to visualize how groundwater flows in 3D along hillslopes, along and around rivers, around weirs and channel confinements, close to the coast, in discharge zones. The terms effective porosity, specific yield, hydraulic conductivity, permeability, transmissivity will be introduced and ranges given for typical aquifers. The properties of porous and fractured aquifers and time scales of aquifer response of groundwater systems will be specified. System characterization for hydrological and groundwater modelling with different physical and hydrochemical methods will be an important aspect.