LER or Ler may refer to:
- Ler, Norway, a village in the municipality of Melhus, Norway
- "Ler" books, a trilogy by M. A. Foster
- Label Edge Router, a term used to define an edge-most router in an IP/MPLS network
- Larry LaLonde, nicknamed "Ler", guitarist of the rock band Primus
- Light-emitting resistor, the working principle of an incandescent light bulb
- Leytonstone High Road railway station, London, England
- Loss Exchange Ratio, a military calculation of comparative casualties of war
- London Electric Railway, later part of the London Underground
- The Loyal Edmonton Regiment, an infantry unit of the Army Reserve Canadian Forces
- Luminous efficacy of radiation, for light sources, the ratio of luminous flux to power
- Lunar Electric Rover, a vehicle designed by NASA for extra-vehicular activity on the lunar surface.
- Elite One Championship (French: Ligue Élite de Rugby), a French rugby league
- Lir, a sea god in Irish mythology also known as Ler
- LER, Local Equipment Room