Arthur H. Hahlo was a New York art dealer and print publisher.
A great number of Whistler etchings passed through Hahlo's hands. He built up strong relations with important Whistler collectors including Howard Mansfield and Harris Whittemore. Mansfield's famous collection of 420 Whistler etchings and 162 lithographs made the headlines in 1919 when it was bought by a private collector through Arthur H. Hahlo & Co. reputably for nearly half a million dollars. It was later reported that the sum was closer to $350,000 and the private collector was Harris Whittemore ('Widdemare' according to the New York Times). Hahlo held exhibitions of contemporary printmakers in his gallery, for which he published small catalogues, for example, Catalogue of etchings by D. Y. Cameron (1912).
Boston Public Library records; New York Times, 5 February 1919, p. 10.