This thesis aimed to examine service contact among children and young people with mental health problems, and has three complementary parts. The first is a secondary analysis of data from the British Child and Adolescent Mental Health Survey (BCAMHS) 2004, which explored mental health related service contact in relation to psychopathology over three years. The second and third parts focussed on young people with ADHD in transition from child services, which is a particularly challenging time. This involved a qualitative interview study of young peoples’ experiences, and an analysis of primary care prescribing of ADHD medication over the transition period using a cohort from the Clinical Practice Research Datalink from 2005-2013. Less than a third of children with a psychiatric disorder in BCAMHS reported contact with child mental health services. Instead, teachers were the most frequently used service, with two-thirds reporting mental health related contact. Interviews with young people with ADHD highlighted themes including concerns around medication management post transition and need for information. The prescribing analysis found that the majority of adolescents on ADHD medication at age 16 stopped during the transition period. This continuing disparity between estimates of symptom persistence and medication persistence suggests that many may be stopping medication from which they could still benefit; as various barriers have been identified to ongoing prescribing. In summary, the findings of these three linked studies suggest common themes in terms of unmet needs and gaps between policy and practice in mental health services for children and young people. One of the chief implications is the need for oversight and policy levers to ensure the implementation of best practice, accompanied by complementary efforts to better understand and overcome other barriers to providing optimal care, including research into knowledge and attitudes of different groups and the provision of targeted training.