The evaluated criticality safety benchmark data in the 2019 edition contains 574 evaluations with benchmark specifications for 4 973 critical, near-critical or subcritical configurations, 45 criticality alarm placement/shielding configurations with multiple dose points for each, and 237 configurations which have been categorised as fundamental physics measurements that are relevant to criticality safety applications. New to the handbook are subcritical experiments with the Inherently Safe Subcritical Assembly (ISSA), carried out in the ISSA laboratory at Lawrence Livermore National Laboratory (LLNL) in the United States.