This textbook provides an in-depth overview of the hydrodynamics of estuaries and semi-enclosed bodies of water. It begins by describing the typical classification of estuaries, followed by a presentation of the quantitative tools needed to study these basins: conservation of mass, salt, heat, momentum, and the thermodynamic equation of seawater. Further topics explore tides in homogeneous basins, including shallow water tides and tidal residual flows, wind-driven flows in homogeneous basins, density-driven flows, as well as interactions among tides, winds and density gradients. The book proposes a classification of semi-enclosed basins that is based on dominant dynamics, comparing forcing agents and restorative or balancing forces. Introduction to Estuarine Hydrodynamics provides an introduction for advanced students and researchers across a range of disciplines - Earth science, environmental science, biology, chemistry, geology, hydrology, physics - related to the study of estuarine systems.