The NZR J class was a class of forty 4-8-2 steam locomotives operated by the New Zealand Railways Department (NZR). Although designed to work on the lighter secondary lines, the class was frequently used on mainline express passenger trains as well as freight. When first introduced, the class boasted distinctive streamlining, which was later removed from 1947 onwards for maintenance reasons. Three of this class remained in service until the end of steam operation on 26 October 1971, when they were withdrawn and entered into preservation. This class should not be confused with the earlier J class from 1874.

The New Zealand Railways Department, NZR or NZGR and often known as the "Railways", was a government department charged with owning and maintaining New Zealand's railway infrastructure and operating the railway system. The Department was created in 1880 and was corporatised on 1 April 1982 into the New Zealand Railways Corporation. Originally, railway construction and operation took place under the auspices of the former provincial governments and some private railways, before all of the provincial operations came under the central Public Works Department. The role of operating the rail network was subsequently separated from that of the network's construction. From 1895 to 1993 there was a responsible Minister, the Minister of Railways. He was often also the Minister of Public Works.