Born on 18 November 1871 at Warren, Pennsylvania, he was the son of a banker and attended Brown University (graduating with an AB degree in 1894) and Harvard Law School (where he earned the LLB in 1898).
[1] Hazeltine's doctoral thesis formed the basis of his first book, Die Geschichte des englischen Pfandrechts, a history of mortgages in English law, published in 1907.
He instigated the Cambridge Studies in English Legal History series in 1921, which he edited for twelve volumes.
He was known for his ability to synthesise existing legal scholarship but made few original contributions or investigations.
[1] After leaving Cambridge, he lived out the remainder of his life in the United States, with an office at Harvard Law School.