An updated edition (with corrections) of Marty Alexander's 1994 report on the criteria used to define the fire danger classes in New Zealand. A fire danger class scheme based on Byram's concept of fire intensity as a yardstick of suppression difficulty was devised for forests and grasslands (and subsequently, scrublands) using the Canadian Forest Fire Behaviour Prediction System. Five fire danger classes are recognized: LOW, MODERATE, HIGH, VERY HIGH, and EXTREME. Inputs include the Initial Spread Index and Buildup Index components of the Fire Weather Index System, and a visual assessment of the Degree of Curing in grasslands. A field application section presents separate tables and graphs for determining Forest and Grassland fire danger classes. A research documentation section describes the derivation of the fire danger class criteria. The classification scheme is designed primarily for fire prevention purposes in connection with the general public (i.e., to inform the lay person of impending fire danger conditions so as to limit the number of potential ignitions. The report is divided into two separate parts for the convenience of the reader: Field Application, and Research Documentation. The Field Application section is for those interested only in the practical aspects of applying the criteria, whereas the Research Documentation section is for those who are interested in how the criteria were derived, and the procedures involved, mathematical analyses and associated philosophical discussion.