The 400Rooms campaign aims at end homelessness in the Brussels-Capital Region by 2020. To achieve this, several associations have decided to unite around a single campaign. Their union aims to go even further than the more traditional - but still necessary - interventions of individual associations. The desire to move forward more quickly, to find more global and permanent solutions has given way to the obligation to act. In view of the magnitude of the challenge, we must find a solution of the same magnitude.