Explore the fundamentals of hydrodynamic stability in this comprehensive lecture by Rama Govindarajan. Delve into key concepts such as linear stability, density stratification, and various instabilities including Rayleigh-Taylor, Rayleigh-Plateau, and Kelvin-Helmholtz. Examine the role of surface tension, polymer flows, and centrifugal forces in fluid dynamics. Gain insights into stability analysis for incompressible Navier-Stokes equations and the significance of Reynolds number. Discover how small changes can lead to large effects in fluid systems, and understand the applications of these principles in geophysical phenomena.