Sir Johann Franz Julius von Haast (May 1, 1822 - August 16, 1887) was a German geologist.

Haast was born at Bonn. He received his early education partly in that town and partly in Cologne, and then entered the university of Bonn, where he studied geology and mineralogy. In 1858 he started for New Zealand to report on the suitability of the colony for German emigrants. He then became acquainted with Ferdinand von Hochstetter, and assisted him in the preliminary geological survey which von Hochstetter had undertaken.

Afterwards Dr Haast accepted offers from the governments of Nelson and Canterbury to investigate the geology of those districts, and the results of his detailed labours greatly enriched our knowledge with regard to the rocky structure, the glacial phenomena and the economic products. He discovered gold and coal in Nelson, and he carried on important researches with reference to the occurrence of Dinornis and other extinct wingless birds (Moa).

His Geology of the Provinces of Canterbury and Westland, N.Z., was published in 1879. He was the founder of the Canterbury museum at Christchurch, of which he became director, and which he endeavoured to render the finest collection in the southern hemisphere. He was surveyor-general of Canterbury from 1861 to 1871, and professor of geology at Canterbury College. He was elected fellow of the Royal Society in 1867; and he was knighted for his services at the time of the colonial exhibition in London in 1887. He died at Wellington, New Zealand.

It was Haast who named the Franz Josef Glacier after the Emperor of the Austro-Hungarian Empire. Several places in New Zealand are named for him, including Haast Pass, the Haast River and the town of Haast. The schist found in New Zealand is called the Haast Schist in tribute to his contributions to geology. He was the first person to study the bones of the extinct Haast's eagle.