Fluids produced from hydrocarbon fields are composed of a mixture of oil, gas and water, often with corrosive components, sometimes laden with solid particles, and are a potential source of many flow instabilities. Frequently, they are now directly exported long distances, in multiphase conditions, towards an existing processing facility or a new processing centre created to serve simultaneously several new fields.This production scheme, which is especially applied offshore, in mature basins such as in the North Sea or in the Gulf of Mexico where infrastructure exists over large areas, can also improve the economics of small or deepwater fields. This book presents the fundamentals of multiphase production with regard to flow simulations in multiphase pipelines, multiphase pumping and multiphase metering. It gives first a description of the multiphase flow patterns that may appear in a pipe and explains how they are managed by the models. It also offers a good introduction to modelling of hydrodynamic effects, thermodynamics and thermal exchanges. Multiphase pumps are now deployed in fields, whether onshore, offshore or subsea, all over the world, where natural reservoir pressure is insufficient.The book presents the various multiphase pump concepts and explains their operating principles and how they can be introduced into a production system. An adequate instrumentation system is needed to monitor and control the performance of such systems and multiphase meters are increasingly used in place of conventional test separators, both offshore and onshore. This book provides the basic principles of multiphase metering, which relies on a combination of elementary measurements, and particularly the means to meter the oil, gas and produced water flowrates in multiphase conditions. The successful application of long-distance multiphase transportation, multiphase pumps and meters has paved the way for the development of subsea processing, presented and discussed in the last chapter which deals with new areas such as subsea separation, subsea gas compression, energy recovery with a multiphase turbine, etc. This book gives a large range of information on approaches and technologies which can be used today. It is designed for engineers involved in field development, but also for petroleum engineering students.