Research on advanced data analysis techniques and unobtrusive measurement modalities are gaining increasing interest in the area of sleep monitoring. The objective of the SOMNIA study is to create a large-scale dataset for the validation of new sleep monitoring techniques against gold standard polysomnography (PSG) in a representative group of sleep clinic patients. Subjects are recruited among patients who are planned for PSG as part of the standard diagnostic process at sleep medicine center Kempenhaeghe. The SOMNIA dataset is a unique dataset containing more than 1700 simultaneously recorded clinical PSG data and sensor data of different novel sensor modalities.