Intelligent Well (IW) technology has built-up several years' production experience. Numerous publications have described how remote flow control and monitoring capabilities can lead to fewer interventions, a reduced well count and improved reservoir management. Despite the maturity of IW equipment, the concept of the integrated IW as a key element in the "Digital Oil Field" still not fully developed. Today's practice is to evaluate the IW value chain in a "fit-for-purpose" manner rather than by an integrated modeling workflow. Reservoir engineers still struggle to convince their management of the IW's value, while the well engineer is only consulted immediately before completion deployment. Hardware and software interface problems result because appropriate technology was not selected.An increasing variety of real-time, downhole, monitoring and measurement systems are now available for deployment or are in development. Sensors for high resolution pressure and temperature, high frequency pressure (acoustic), multiphase flow rate, phase-cut, electric potential (electro-kinetic), seismic (accelerometers) and casing condition monitoring (strain) are all now (at least semi-) commercial; not to mention the option of installing quasi-distributed and/or distributed rather than a single point measurement. The former sensors provide a wealth of information about flow performance and in-well and nearwellbore formation conditions. However, each extra sensor increases the well's installation complexity and operational risk. A well-founded understanding of what data is actually needed; the most suitable sensor types and interfaces together with avail liability of the necessary data reconciliation and validation methodology are key factors for the success of an integrated IW project.This paper will review intelligent well monitoring systems, their availability, applicability and limitations. It will discuss data acquisition issues in-depth; e.g. resolution, data processing and reliability. Examples of fit-for-purpose sensor/data sets applicable to different IW applications will be given. This paper will guide the completion engineer to identify the appropriate set of downhole sensors for a specific, integrated, IW application.