In Star Trek chronology, the Day of Honor is a festival when all "true Klingons" re-affirm their own sense of honor and commemorate the honor of their most esteemed enemies. It is known as Batlh Jaj in tlhIngan Hol.
The origin dates back to when Captain James T. Kirk of the United Federation of Planets and Commander Kor of the Klingon Empire formed an uneasy alliance. The Klingon planet of QI'tu' (or Signi Beta, as it was known to the Federation) was under siege by an unknown enemy. By providing assistance and constantly putting the lives of his crew in danger, Captain Kirk won over the trust of the Klingons who learnt that even their enemies may have a sense of honor.
It was first mentioned in the episode Day of Honor (VOY) and soon spawned a best-selling series of books conceptualised by John J. Ordover and Paula M. Block. All books were published by Pocket.
The series of books consisted of:
- Ancient Blood by Diane Carey - Based on characters from The Next Generation.
- Armageddon Sky by L.A. Graf - Based on characters from Deep Space Nine.
- Her Klingon Soul by Michael Jan Friedman - Based on characters from Voyager.
- Treaty's Law by Dean Wesley Smith and Kristine Kathryn Rusch - Based on characters from Star Trek: The Original Series.
- Day of Honor by Michael Jan Friedman - Based on the episode's teleplay by Jeri Taylor.
- Honor Bound by Diane G. Gallagher - Based on characters from Deep Space Nine.
The books depict various reactions to the Day of Honor, from human-raised Klingon Worf's determination towards celebrating it properly, to half-Klingon B'Elanna trying to survive the "unluckiest day of her year".
But the best book of the series, other than Treaty's Law which recounts the actual origin of the festival itself, has to be the Deep Space Nine novel, Armageddon Sky. In the story, The Defiant is sent to investigate a cataclysmic world which happens to be the home of a House of Klingons, exiled in disgrace by the Empire. Together with Dahar Master Kor, they uncover a significant threat to the Klingon Empire, as well as re-discovering the honor in each other's cultures. | 
