Time-lapse seismic surveys or 4D seismic offers snapshots of a producing hydrocarbon reservoir and its surroundings and is the most common seismic surveillance technique in the oil and gas industry. New developments of this technology includes permanent seismic installations; observations of changes outside the reservoirs and a link to geomechanics and the use of passive recordings. In this book we are using examples from the Valhall field to illustrate examples of seismic surveillance that will include data examples from marine towed 4D, frequent surveying using permanently installed sensors, in-well recordings and analysis of passive data, including micro seismicity. Some of the historical 4D examples, an update on the state of use of permanent recordings systems are also discussed.