The Ministry of Justice Data First prisoner custodial journey dataset provides data on people held in custody in prisons and young offenders institutions (YOIs) in England and Wales, and has been extracted from the management information system Prison National Offender Management Information System (P-NOMIS), used by Her Majesty's Prisons and Probation Service (HMPPS) within prisons. Data on offenders serving custodial sentences since 2011 is expected to be complete, but sentences begun before this are included. Young Offenders are included if resident at prisons or YOIs that use P-NOMIS, however, this excludes the majority of Secure Schools and Secure Training Centres. Information on offender characteristics, their main offence, sentence and release is included: for example age, gender, ethnicity, offence category, and key dates, providing information on movements through the system and their release and recall (if applicable). Each record in the dataset gives information about a single person and custodial journey. As part of Data First, records have been deidentified and deduplicated, using our probabilistic record linkage package, Splink, so that a unique identifier is assigned to all records believed to relate to the same person, allowing for longitudinal analysis and investigation of repeat appearances. This aims to improve on links already made within the prison system. This opens up the potential to better understand the prison population and address questions on, for example, patterns associated with short repeated custodial sentences and what works to reduce reoffending. The Ministry of Justice Data First linking dataset can be used in combination with this and other Data First datasets to join up administrative records about people from across justice services (courts, prisons and probation) to increase understanding around users' interactions, pathways and outcomes.