Udo-Nestor Ivask (December 20, 1878 – May 15, 1922)[1] was an Estonian bibliophile, book historian, and bookplate artist.

After graduating from high school, Ivask went to Moscow, where he studied at the painting studio of Konstantin Korovin.

He wanted to study art, but he was not accepted at the Moscow School of Painting, Sculpture and Architecture[3] due to his age.

[3][4] He founded the Moscow Bookplate Society (Russian: Московское общество любителей книжных знаков) in 1905.

[1][3] He contributed to the creation of the Russian Book Chamber,[1] edited a magazine, and was the head of the department of rare publications at the Rumyantsev Museum and a member of the bibliographic commission of the State Publishing House.