House of Suns is a 2008 science fiction novel by Welsh author Alastair Reynolds. The novel was shortlisted for the 2009 Arthur C. Clarke Award.

Approximately six million years in the future, humanity has spread throughout the Milky Way galaxy, which appears devoid of any other organic sentient life. The galaxy is populated by numerous civilizations of humans and posthumans of widely varying levels of development. A civilization of sentient robots known as the Machine People coexists peacefully with humanity. Technologies of the era include anti-gravity, inertia damping, force fields, stellar engineering, and stasis fields. Also of note is the "Absence"—the mysterious disappearance of the Andromeda Galaxy.

Large-scale human civilizations almost invariably seem to collapse and disappear within a few millennia (a phenomenon referred to as "turnover"), the limits of sub-lightspeed travel making it too difficult to hold interstellar empires together. Consequently, the most powerful entities in the galaxy are the "Lines"—familial organizations made of cloned "shatterlings". The Lines do not inhabit planets, but instead travel through space, holding reunions after they have performed a "circuit" of the galaxy; something that takes about 200,000 years.

House of Suns concerns the Gentian Line, also known as the House of Flowers, composed of Abigail Gentian and her 999 clones (or "shatterlings"), male and female: exactly which of the 1,000 shatterlings is the original Abigail Gentian is unknown. The clones and Abigail travel the Milky Way Galaxy, helping young civilizations, collecting knowledge, and experiencing what the universe has to offer. Members of the Gentian Line are named after flowering plants.

The novel is divided into eight parts, with the first chapter of each part taking the form of a narrative flashback to Abigail Gentian’s early life (six million years earlier, in the 31st century), before the cloning and the creation of the Gentian Line. Each subsequent chapter is narrated from the first-person perspective of two shatterlings named Campion and Purslane, alternating between them each chapter. Campion and Purslane are in a relationship, which is frowned upon, even punishable, by the Line.

The primary storyline begins as Campion and Purslane are roughly fifty years late to the 32nd Gentian reunion. They take a detour to contact a posthuman known as ‘Ateshga’ in hopes of getting a replacement ship for Campion because his is getting old (several million years old). After being tricked by Ateshga, Campion and Purslane manage to turn the tables on him and leave his planet with a being he had been keeping captive, a golden robot called Hesperus. Hesperus is a member of the "Machine People", an advanced civilization of robots, and supposedly the only non-human sentient society in existence. The two shatterlings hope that the rescue of Hesperus will let them off the hook for their lateness, as returning him to his people (who will be at the reunion as guests of other shatterlings) will put the Gentian Line on good terms with the Machine People.

However, before reaching the reunion world, Campion and Purslane encounter an emergency distress signal from Fescue, another Gentian shatterling. There was a vicious attack on the reunion world; an ambush in which the majority of the Gentian Line was wiped out. The identity of the responsible party is unknown, but the attackers used the supposedly long-vanished 'Homunculus' weapons – monstrous spacetime-bending weapons that were created ages ago, but were ordered to be destroyed by another Line.

Despite Fescue's warning, Campion and Purslane approach the reunion system to look for survivors. They manage to find the remains of a ship with several Gentian members still alive, and rescue them and the four enemy prisoners they had captured. Hesperus, however, is gravely injured in the process by remaining ambushers. The group escapes and make their way to the Gentian backup meeting planet, Neume, in the hope of re-grouping with any other Gentians who may have survived the ambush.