ABSTRACT Logging While Drilling (LWD)* tools are formation evaluation sensors engineered into drill collars. Using LWD in horizontal wells offers significant advantages over other logging systems for formation evaluation. When LWD is provided in real-time via mud pulse telemetry the system becomes a geological steering tool which can be used to accurately place the horizontal section with reference to formation features and/or fluid contacts. The combined benefits of formation evaluation and real-time geological steering make LWD an essential tool for many horizontal wells. We will describe the benefits of LWD measurements and the improvements in both drilling and logging efficiency which LWD offers. These features are illustrated with practical examples of LWD from a number of horizontal wells in the North Sea. Although these examples are from horizontal wells in particular, the same benefits can be realized in directional wells in general.