This report explores how Scotland can strengthen its approach to preventing substance use and related harms among young people (defined here as <25 years). While prevention is increasingly recognised as a public health priority, Scotland currently lacks a coordinated, evidence-based prevention system. Public Health Scotland (PHS) is developing a whole-systems approach, and this report aims to contribute by synthesising evidence on effective interventions and conditions for sustainable prevention. The report focuses on non-school-based prevention which includes community, family, digital, and service-based approaches.