This paper describes an analysis of wake measurements from the research farm at the ECN Wind Turbine Test Site Wieringermeer. This research farm is owned and operated by the Energy Research Centre of the Netherlands. The farm consists of five research turbines that are oriented in a single line with a mutual distance of 3.8D(iameter). The turbines are variable speed and pitch controlled, and they have a diameter and a hub height of 80 m. The rated power of the turbines is 2.5 MW. Extensive machine measurements (power, loads, yaw angle and pitch angles) are carried out on these turbines. In parallel, meteorological measurements are done on a 108 m mast that is instrumented at three heights (hub height and hub height ± 70% span) with sonic anemometers and cups and wind vanes. This mast is located at a shortest distance of 2.5D from one of the turbines. Data have been collected over a period of almost 5 years, and they are used to study several phenomena mainly related to wake aerodynamics, e.g. power losses in the wake of up to four wind turbines and meteorological wake phenomena at different distances behind the turbines. Copyright © 2011 John Wiley & Sons, Ltd.