In a series of papers published nearly 60 years ago, Donald Pritchard established the basic understanding of estuarine dynamics. Pritchard’s elegant and simple representations of the subtidal estuarine circulation and salt balance remain the foundation for modern research on physical oceanography in estuaries. Yet, the simplicity of this early work belies the complexity of physical processes that occur in the estuarine environment, complexity that is well articulated in the recent text Contemporary Issues in Estuarine Physics, edited by Arnoldo Valle-Levinson. The book grew out of a 2007 two-week summer program organized by Valle-Levinson through the Pan-American Advanced Studies Institutes (PASI) Program. Leaders in the field of estuarine dynamics were invited to Puerto Morelos, Mexico, to give lectures to graduate and postgraduate researchers from throughout the Americas. Nearly all of the invited lecturers contributed chapters to this book. Consistent with the target audience of the PASI program, this book is intended for graduate students and researchers in the field of oceanography. While some of the information may be relevant to a wider audience, full appreciation of the wealth of information contained in these pages requires at least basic knowledge of physical oceanography. It is assumed that the reader is familiar with fundamental concepts such as conservation of mass and momentum, the role of Earth’s rotation, and Reynolds averaging, as well as mathematical concepts ranging from basic calculus to more advanced techniques including differential equations and perturbation theory.