New Zealand Steel Limited is the owner of the Glenbrook Steel Mill, a steel mill located 40 kilometres south of Auckland, in Glenbrook, New Zealand. The mill was constructed in 1968 and began producing steel products in 1969. Currently, the mill produces 650,000 tonnes of steel a year, which is either used domestically or exported. Over 90% of New Zealand's steel requirements are produced at Glenbrook, while the remaining volume is produced by Pacific Steel, a steel recycling facility in Ōtāhuhu, Auckland. The mill is served by the Mission Bush Branch railway line, which was formerly a branch line to Waiuku. Coal and lime trains arrive daily. Steel products are also transported daily. The mill employs 1,150 full-time staff and 200 semi-permanent contractors.

Glenbrook is a rural and industrial area in the Auckland region of New Zealand. The industrial area, that of New Zealand's major steel mill, New Zealand Steel, is not located close to any towns - the surrounding countryside is occupied by farms. The nearest towns are Waiuku, five kilometres to the south, and Pukekohe, 15 kilometres to the east.