Particle swarm optimization is an upcoming evolutionary algorithm used extensively in water resources engineering. In groundwater hydrology in this book it is used to optimize cost of installing pumping wells to meet the groundwater demand in agriculture, municipal and industrial sectors. Its variants are also applied for optimal cost comparisons. Differential evolution is relatively more recent evolutionary meta-heuristic which is suitable for non-linear, non-differential discrete objective functions. Constraints are incorporated by penalty function. Inverse modeling is essential for aquifer system parameter estimation. Transmissivity, aquifer recharge and storage coefficient are assessed for a confined aquifer by DE. Problems in both sections require simulation-optimization modeling where aquifer system simulation engages finite element technique which is covered in the book apart from details of PSO and DE optimizers.