Henry Martyn Blossom, Jr. (May 10, 1866 – March 23, 1919) was an American writer, playwright, novelist, opera librettist, and lyricist. He first gained wide attention for his second novel, Checkers: A Hard Luck Story (1896), which was successfully adapted by Blossom into a 1903 Broadway play, Checkers. It was Blossom's first stage work and his first critical success in the theatre. The play in turn was adapted by others creatives into two silent films, one in 1913 and the other in 1919, and the play was the basis for the 1920 Broadway musical Honey Girl. Checkers was soon followed by Blossom's first critical success as a lyricist, the comic opera The Yankee Consul (1903), on which he collaborated with fellow Saint Louis resident and composer Alfred G. Robyn. This work was also adapted into a silent film in 1921. He later collaborated with Robyn again; writing the book and lyrics for their 1912 musical All for the Ladies.

Blossom had a lengthy and fruitful partnership as a librettist for the operetta composer Victor Herbert. He began his collaboration with Herbert with Mlle. Modiste (1905). This was followed by several other operettas, of which the best known are Mlle. Modiste (1905), The Red Mill (1906), The Princess Pat (1915), and Eileen (1917). For the 1916 musical The Century Girl, both he and Herbert collaborated with composer Irving Berlin. He also collaborated with Herbert on the musicals The Only Girl (1914) and The Velvet Lady (1919). The latter work premiered shortly before Blossom's death in 1919 and marked their final collaboration. Several of their works have been adapted into films.

Blossom also wrote the lyrics and books for Broadway musicals made with composers Leslie Stuart, Raymond Hubbell, and Zoel Parenteau. He was also involved with several shows that failed to reach Broadway.