The central theme of this book is how ideas familiar from finite dimensional dynamical systems may be used in the study of infinite dimensional dynamical systems, such as partial differential equations. After an introduction to the study of partial differential equations from the perspective of dynamical systems, some of the ideas are applied to the equations of fluid dynamics and the application of low-dimensional models of turbulence. A discussion of chaos in lattice dynamical systems (for which the spatial dimension is discrete) is followed by the use of such models in biology.