We explore trends in youth justice and penality over a 40-year period. We begin by focusing on what we term the ‘ebbs and flows’ of child and youth imprisonment, before turning our attention to the more general temporal and spatial patterning of youth justice and penality over three discrete periods. First circa 1980–1991, a period in which the imperatives of diversion and decarceration prevailed, and youth justice and penality in Australia and in England and Wales was characterised by convergent and confluent forms. Second circa 1992–2002, a decade during which divergence and difference became more apparent. As the principles of diversion and decarceration consolidated within youth justice in Australia, conditions in England and Wales were marked by the manifest politicisation of youth crime, and policy and practice took a decisively punitive turn. Third circa 2003–2018, a period when a mélange of competing and even contradictory priorities – including ‘what works’ logics; actuarial priorities, risk assessment and risk management strategies; punitiveness and intolerance and various spatially and temporally defined counter-motions – gave rise to incoherence and messiness. In sum, we argue that the various forms that youth justice and penality assumes are best understood as political as distinct from penological adaptations.