Book excerpt: The most important processes on the Earth`s surface occur in the Ocean where materials and energy are primarily exchanged. In the case of marine chemistry different fields of chemistry from organic to inorganic as well as thermodynamics and biochemistry are involved. Analytical Chemistry is a very important tool for the quantification of biogeochemical processes by providing correct and even more sophisticated methodologies. These are often directly applied 'in situ', in order to detect trace and ultra-trace natural and anthropogenic substances. Kinetic and thermodynamic studies allow us to establish whether the process occurs. Once discovered it is then possible to build up general models for environmental systems. This book gathers many aspects with the aim of creating a general picture of the chemical processes occurring in the marine environment