The fourth issue of this series deals with the current topic “Airbnb and Co.”. The original idea of sharing a couch space that has become temporarily vacant is increasingly being transformed into a professional business model in which individual rooms and apartments are rented out on a daily or weekly basis throughout the year. The authors from the ILS research group “Spatial Planning and Urban Design” and from the TU Dortmund University are therefore investigating the questions of what influence such short-term rentals have on urban structures, how the corona pandemic is affecting this market, and what regulatory and action options exist for cities.