Diomedes is a fictional water world in Poul Anderson's Polesotechnic League universe.
A large, metal-poor (1.1g) world, Diomedes is home to one of the two known races of flying sophonts, who divide themselves into the Lannach'Ho and the Drak'ho. The Lannach'ho call it "Ikt'thanis", which literally translates as "Oceanest". Its inner moon is known as "Flichton" to the Lannach'ho and as "Sk'huanax" (the warrior god) to the Drak'ho. Its outer moon is known as "Nua" to the Lannach'ho and as "Lykharis" (the mother god) to the Drak'ho. The Sea of Achan is bounded by Lannach and the Homenach Archipelago. Mannenach and Salmenbrok, two Drak'ho towns, are located on this sea's Sagna Bay. The firm Solar Spice and Liquors had a trading post on Diomedes, located at Thursday Landing.
- Van Rijn was stranded there in 2426. (The Man Who Counts)
- Dennitza was framed with instigating rebellion there in 3047. (A Knight of Ghosts and Shadows)