The WHO Mental Health Gap Action Programme (mhGAP) guideline update reflects 15 years of investment in reducing the treatment gap and scaling up care for people with mental, neurological, and substance use (MNS) conditions. It was produced by a guideline development group and steering group, with support from topic experts, using quantitative and qualitative evidence and a systematic review of use of mhGAP. 90 recommendations from the 2015 guideline update were validated and endorsed for use in their current format. These are joined by 30 revised recommendations and 18 new recommendations, including a new module on anxiety. Psychological interventions are emphasised as treatments and digitally delivered interventions feature across many modules, as well as updated recommendations for psychotropic medicines. Research gaps identified include the need for evidence from low-resource settings and on the views of people with lived experience of MNS conditions. The revised recommendations ensure that mhGAP continues to offer high-quality, timely, transparent, and evidence-based guidance to support non-specialist health workers in low-income and middle-income countries in providing care to individuals with MNS conditions.