Rosenberg began publishing with his story "Like the Gentle Rains," which appeared in Isaac Asimov's Science Fiction Magazine in 1982. The following year, he published his first novel, The Sleeping Dragon which was the first in his long-running "Guardians of the Flame" series. This series placed a collection of college students into a Medieval fantasy setting similar to a role-playing world. Throughout numerous books, Rosenberg has traced these characters, their descendants and the changes they've made to society. He has shown no compunction about killing off popular characters.
The "Keepers of the Hidden Ways" trilogy similarly places people from the real world into a fantasy setting, making heavy use of Norse mythology. A third fantasy series, comprised of the novels D'Shai (1991) and Hour of the Octopus (1994) (both lightly humorous mysteries) is set in a Asian-influenced fantasy world with very strict cultural standards and etiquette. A third D'shai novel is currently in pre-publication.
In addition to fantasy, Rosenberg has published a number of science fiction novels. Although dealing with different characters, Ties of Blood and Silver (1984) and Emile and the Dutchman (1986) are both set in the same universe. Two other books set in this universe, Not for Glory (1988) and Hero (1990) focus on a band of Jewish mercenaries in space.
Rosenberg's novels frequently features a theme of protecting children at all costs and depicts the way people can overcome hardships and abuse suffered as children.