LGS may refer to:
Education Lahore Grammar School Lanark Grammar School Langley Grammar School Larne Grammar School Leeds Grammar School Leicester Grammar School Limavady Grammar School Loughborough Grammar School
Entertainment Looking Glass Studios, a defunct computer game company La Grande Sophie, a French singer-songwriter
Science Laser guide star, an adaptive optics instrument used in astronomy Latitudinal gradients in species diversity Leaky gut syndrome, an intestinal dysfunction LGS Innovations, a high-tech private company and former division of Bell Labs Lennox–Gastaut syndrome, a type of epilepsy
Software Liberty Steel Group, a British industrial and metals company