The book describes the progress made in understanding the phenomena of various hydrodynamic instabilities over the last thirty years. Exact results for the onset of Rayleigh-Benard convection in different systems are presented and approximation techniques like amplitude equations and few-mode truncations are treated at length. Routes to chaos and the characteristics of the chaotic state are reviewed. Certain features of the Taylor-Couette flow and the effect of parametric modulation on hydrodynamic instabilities are discussed. The theory is supplemented by experimental results.