Vatta's War is a science fiction series by American writer Elizabeth Moon, comprising five books: Trading in Danger (2003), Marque and Reprisal (2004) (Moving Target in UK and Australia), Engaging the Enemy (2006), Command Decision (2007), and Victory Conditions (2008). They have been characterized as military science fiction similar in style to the works of Lois McMaster Bujold (Vorkosigan Saga), David Weber and Walter Jon Williams (Dread Empire's Fall).

The books follow the adventures of Kylara Vatta, a young member of the Vatta family, which runs the interstellar shipping corporation Vatta Enterprises. She had sought a life outside the family business by enrolling in the Slotter Key Spaceforce Academy, but she is forced to resign in her final year and assigned to captain an old trading ship for the corporation. Her military training is put to good use, however, during the crises she faces, first as a ship captain in dangerous situations, and later as the representative of a family under attack.

The first book, Trading in Danger, is narrowly focused on Ky and the local crisis in which she becomes involved. The perspective expands in the later books as connections between piracy and ansible attacks on the one hand and Vatta Enterprises and InterStellar Communications Corporation (ISC) on the other are revealed. In 2017 Cold Welcome was published. It is the first book of the new Vatta's Peace series. It also features Kylara Vatta and is set after the events of Vatta's War.