Battlestar Galactica is an American military science fiction television series, and part of the Battlestar Galactica franchise. The show was developed by Ronald D. Moore and executive produced by Moore and David Eick as a "re-imagining" of the 1978 Battlestar Galactica television series created by Glen A. Larson. The pilot for the series first aired as a three-hour miniseries in December 2003 on the Sci-Fi Channel, which was then followed by four regular seasons, ending its run on March 20, 2009. The cast includes Edward James Olmos, Mary McDonnell, Katee Sackhoff, Jamie Bamber, James Callis, Tricia Helfer, and Grace Park.

Battlestar Galactica is set in a distant star system, where a civilization of humans live on a group of planets known as the Twelve Colonies of Kobol. In the past, the Colonies had been at war with an android race of their own creation, known as the Cylons. With the unwitting help of a human scientist named Gaius Baltar (Callis), the Cylons launch a sudden sneak attack on the Colonies, laying waste to the planets and devastating their populations. Out of a population of several billion, there are about 50,000 human survivors; most were aboard civilian space ships that were not near the initial attacks. Of all the Colonial Fleet, the Battlestar Galactica (an older ship about to be decommissioned and turned into a museum) appears to be the only military capital ship that survived the attack. Under the leadership of Colonial Fleet officer Commander William "Bill" Adama (Olmos) and President Laura Roslin (McDonnell), the Galactica and its crew take up the task of leading the small fleet of refugee survivors into space in search of a fabled thirteenth colony known as Earth.

The series received critical acclaim at the time and since, including a Peabody Award, the Television Critics Association's Program of the Year Award, a placement inside Time's 100 Best TV Shows of All-Time and 19 Emmy nominations for its writing, directing, costume design, visual effects, sound mixing and sound editing, with three Emmy wins (visual effects and sound editing). In 2019, The New York Times placed the show on its list of "The 20 Best TV Dramas Since The Sopranos", a period many critics call a "golden age of television".

The series was followed by the prequel spin-off TV series Caprica, which aired for one season in 2010. A further spin-off, Battlestar Galactica: Blood & Chrome, was released in November 2012 as a web series of ten 10-minute episodes and aired on February 10, 2013, on Syfy as a televised movie.

Battlestar Galactica continued from the 2003 miniseries to chronicle the journey of the last surviving humans from the Twelve Colonies of Kobol, after their nuclear annihilation by the Cylons. The survivors are led by President Laura Roslin and Commander William Adama in a ragtag fleet of ships with the Battlestar Galactica, an old but powerful warship, as its command ship. Pursued by Cylons intent on wiping out the remnants of the human race, the survivors travel across the galaxy looking for the fabled and long-lost "thirteenth" colony: Earth. Unlike most space opera series, Battlestar Galactica has no humanoid aliens (the antagonists are man-made Cylon androids), the primary armaments used by both military forces utilize bullets, rail guns, and missiles instead of lasers, and the series intentionally avoids technobabble. Instead, most of the stories deal with the apocalyptic fallout of the destruction of the Twelve Colonies upon the survivors, and the moral choices they must make as they deal with the decline of the human race and their war with the Cylons. Stories also portray the concept of perpetuated cycles of hate and violence driving the human-Cylon conflict, and religion, with the implication of a "God" whose possibly angelic agents appear to certain main characters (most notably Gaius Baltar).

Over the course of the show's four seasons, the war between the Colonials and the Cylons takes many twists and turns. Despite the animosity on both sides, the humans and a faction of the Cylons eventually form an uneasy alliance, in the wake of the Cylon Civil War. The Cylon leader, a Cylon-humanoid "Number One" named John Cavil, precipitated the schism in the Cylon ranks. Cavil deceives the other models by obsessively hiding the identities and origins of the remaining five humanoid Cylon models, the "Final Five", who, known only to him, are a more ancient type of Cylon, created by a previous iteration of human civilization. Other plotlines involve the mysterious destiny of Kara "Starbuck" Thrace, who is the subject of a prophecy claiming that she is the "Harbinger of Death" who will "lead them all [humanity] to its end", as well as the redemption of Gaius Baltar through the Cylons' monotheistic religion, after he becomes a pariah within the fleet.

In the final episodes, an inexplicably resurrected Kara Thrace leads the surviving humans and their Cylon allies to a new planet, which Adama names "Earth". The first group of survivors settle in ancient Africa. The "real" Earth that the Colonials had searched for during their years in space was revealed in an earlier episode to have been originally inhabited thousands of years before by a previous form of humanoid Cylons; the "Final Five" were the last of these Cylons. Ironically, these humanoid Cylons had created their own Centurion robotic slaves, who waged a nuclear attack against their masters, devastating the planet and making it uninhabitable. The new Earth is found to be inhabited by early humans, who are genetically compatible with the humans from Galactica and the rest of the fleet, but who possess only the most rudimentary civilization.

The surviving humans and humanoid Cylons settle on the new planet Earth; they discard all technology, destroying the fleet by flying it into the Sun, in an attempt to break the human-Cylon cycle of conflict and begin anew with the tribal humans already present on the new Earth. The surviving Cylon Centurions are given possession of the remaining Cylon Basestar, and proceed to jump away from Earth. In the final scenes, modern-day Earth humans are shown to be descendants of the colonists, their humanoid Cylon allies, and the early humans.