In the Star Trek fictional universe, LCARS (an acronym for Library Computer Access and Retrieval System, pronounced "ELL cars"), is a computer operating system used on Federation starships. Within Star Trek chronology, the term was first used in Star Trek: The Next Generation and in subsequent shows. In a real-world context, the term "LCARS" is frequently used to describe the style of the computer displays of the LCARS system, especially the screens from The Next Generation. The term "Okudagrams," named for Michael Okuda, the designer of the graphics, is also used to refer to this style. The design is popular among Star Trek fansites.

The LCARS GUI was designed by scenic art supervisor and technical consultant Michael Okuda. The original design concept was influenced by a request from Gene Roddenberry that the instrument panels not have a great deal of activity on them. This minimalized look was designed to give a sense that the technology was much more advanced than in the original Star Trek. The early display panels were made out of colored Plexiglas with light behind them. This can produce complex looking displays very cheaply.

LCARS in Enterprise E, from Star Trek Movie, Nemesis.