In 2004 a new model of working practice between three public sectors, the local Police Department, Social Services and Psychiatry/Mental Health Services (PSP) was introduced in the municipality of Frederiksberg, Denmark. The aim of this cooperation was to enhance support to vulnerable citizens, who do not belong solely to one of the three sectors and thereby often get lost in the system. The PSP cooperation was introduced to ensure that relevant information concerning vulnerable citizens was shared between the three sectors and to improve collaboration between the sectors involved in order to provide the needed support to the individual citizen. Due to the success of the PSP cooperation in Frederiksberg, the PSP model was implemented by law in Denmark in 2009. In order to evaluate the model, a qualitative study based on structured interviews, focus group discussions and observations, was performed in four selected municipalities in Denmark: Frederiksberg, Odense, Amager and Esbjerg. The evaluation was undertaken by the Danish National Centre for Social Research. It is concluded that the PSP cooperation draws attention to marginalized groups of citizens and helps to prevent social downfall and crime. Participants of the PSP cooperations further highlight positive changes in the cooperation between the involved sectors, which is thought to further improve the support to vulnerable citizens and thereby enhance both prevention and follow up of cases. Furthermore, the recommendations drawn from the evaluation are to adapt PSP cooperations to local conditions, avoid unnecessary red-tape, keep a constant focus on citizens' ethics, as well as involve the frontline workers in the individual sectors, i.e. those who are actually in contact with marginalized citizens.