The scientific literature indicates that the use of drugs among people with mental illness (MI) varies from 20 to over 50%, while mental health disorders are also common among people with substance use disorders (SUD). People with both SUDs and MI face greater difficulties than those with one issue alone, in terms of access to services, unmet needs, compliance to treatment or relapses, social integration and personal recovery. Their medical, psychological and social needs require comprehensive care from healthcare providers, particularly in terms of continuity and personalised care. However, in Belgium, as in other countries, care provision for these populations is divided into separate sectors, a generic mental health care sector and a sector specialised in addiction. The SUMHIT study therefore examined the needs of users of both types of service, as well as the experiences of users and professionals in accessing and delivering care. In addition, SUMHIT examined the organisational capacity of the two sectors to collaborate and integrate within the general framework of service networks implemented within the 'psy 107' reform. Five areas were selected for the study: Antwerp (SaRA), Aalst-Termonde-St-Nicolas (GGZ ADS), and South-West Flanders (GGZ ZWVl) in Flanders; Brumenta (the Brussels network, which is made up of 4 sub-networks: Bruxelles-Est, Hermes+, Rézone, and Norwest); and the 'Réseau Santé Namur' in Wallonia. In these five areas, a number of research actions were carried out: a survey of 562 service users about their care and support met and unmet needs; 53 qualitative interviews were also conducted with service users and people who were no longer in contact with the care system. At the professional level, a survey of the organisation of services was completed by 194 generic and specialised services, and focus groups were organised with professionals and experts by experience. Finally, a literature review was carried out on interventions facilitating the personal recovery of users with substance use ...