How do we know what happens inside our jails? This talk will describe the history and role of HMI Prisons and set this in the context of the UK's obligations arising from its status as a party to the Optional Protocol to the Convention Against Torture and other Cruel, Inhuman and Degrading Treatment or Punishment (OPCAT). It will argue for the importance of independent, human rights based inspection not just as an accountability mechanism but as a preventative process. 'Knowing' what happens changes what happens. The talk will also discuss current inspection findings, focussing mainly on the adult prison estate and consider the impact of current policy including 'Transforming Rehabilitation' polices, resource constraints, population pressures and restrictions on prisoners' regime and privileges. It will assess the extent to which the system is coping with the pressures these factors create.