Many factors influence students' experiences in upper secondary education and beyond, including upper secondary curricula, programme design and support for students. But a good transition from earlier levels of education is the first, essential step in a successful journey through upper secondary education and into further education and/or employment. The design of transition systems can mitigate existing inequities in education, but it can also accentuate them. Transitions can also influence student well-being. They can have either a negative impact, for example through highly competitive systems that can be stressful for students and narrow their development, or a positive impact, for example by helping to construct young people's sense of agency and ability to make informed decisions about their future. This paper looks at how countries manage students' transition into upper secondary education and the main policy implications of each transition point and how they can influence student outcomes.