The Alcubierre drive is the only known method of faster-than-light technology and thus forms the basis of interstellar civilization. It is named after a similar technology that was theorized by Miguel Alcubierre during the 20th century.
The Alcubierre drive functions by creating a bubble of warped space around the drive (and the spaceship) that propagates across space faster than the speed of light, carrying the spaceship along with it.
An Alcubierre bubble's maximum speed of propagation is limited by the bubble's size, which in turn is limited by the size of the vessel. The fastest ships can reach speeds of .54 LY/day.  The largest ships capable of interstellar travel are the colony ships operated by Imperial China, which have a maximum speed of 0.09 LY/day.
In addition, an Alcubierre bubble will collapse if not constantly maintained by an Alcubierre drive, making it unsuitable for wireless FTL communication. Human civilization is instead forced to rely on a web of small, fast courier vessels for communication between planets.