A red light camera (short for red light running camera) is a type of traffic enforcement camera that captures an image of a vehicle which has entered an intersection in spite of the traffic signal indicating red (during the red phase). By automatically photographing vehicles that run red lights, the photo is evidence that assists authorities in their enforcement of traffic laws. Generally the camera is triggered when a vehicle enters the intersection (passes the stop-bar) after the traffic signal has turned red. Typically, a law enforcement official will review the photographic evidence and determine whether a violation occurred. A citation is then usually mailed to the owner of the vehicle found to be in violation of the law. These cameras are used worldwide, in countries including: Australia, New Zealand, Canada, the United Kingdom, Singapore and the United States. If a proper identification cannot be made, instead of a ticket, some police departments send out a notice of violation to the owner of the vehicle, requesting identifying information so that a ticket may be issued later.

 There is debate and ongoing research about the use of red light cameras. Authorities cite public safety as the primary reason that the cameras are installed, while opponents contend their use is more for financial gain. There have been concerns that red light cameras scare drivers (who want to avoid a ticket) into more sudden stops, which may increase the risk of rear-end collisions. The elevated incentive to stop may mitigate broad-side crashes. Some traffic signals have an all red duration, allowing a grace period of a few seconds before the cross-direction turns green. Some studies have confirmed more rear-end collisions where red light cameras have been used, while broad-side crashes decreased, but the overall collision rate has been mixed. In some areas, the length of the yellow phase has been increased to provide a longer warning to accompany the red-light-running-camera. There is also concern that the international standard formula used for setting the length of the yellow phase ignores the laws of physics, which may cause drivers to inadvertently run the red phase.

As of December 2016 Arizona, Arkansas, Louisiana, Maine, Mississippi, Montana, Nevada, New Jersey, South Carolina, South Dakota, Utah, West Virginia and Wisconsin have enacted various prohibitions on red light, speed or other photo enforcement camera uses. Restrictions or conditions exist in additional states; the New Mexico Department of Transportation, for example, has asserted the right to restrict or prohibit red light cameras on state highways. While red light cameras may not be prohibited in other regions, they may have some restrictions on their use. In some jurisdictions, the law says that the camera needs to obtain a photo of the driver's face in order for the citation issued for running the red light to be valid. This is the case in California and Colorado where the red light cameras are set up to take a series of photographs, including one of the driver's face. In California, state law assesses a demerit point against a driver who runs a red light, and the need to identify the actual violator has led to the creation of a unique investigatory tool, the fake "ticket." Groups opposing the use of red light cameras have argued that where the cameras are not set up to identify the vehicle driver, owner liability issues are raised. It is perceived by some that the owner of the vehicle is unfairly penalized by being considered liable for red-light violations although they may not have been the driver at the time of the offense. In most jurisdictions the liability for red light violations is a civil offense, rather than a criminal citation, issued upon the vehicle owner—similar to a parking ticket. The issue of owner liability has been addressed in the US courts, with a ruling in the District of Columbia Court of Appeals in 2007, which agreed with a lower court when it found that the presumption of liability of the owners of vehicles issued citations does not violate due process rights. This ruling was supported by a 2009 7th US Circuit Court of Appeals ruling in which it was held that issuing citations to vehicle owners (or lessees) is constitutional. The court stated that it also encourages drivers to be cautious in lending their vehicles to others.

The argument that red light cameras violate the privacy of citizens, has also been addressed in the US courts. According to a 2009 ruling by the 7th US Circuit Court of Appeals, “no one has a fundamental right to run a red light or avoid being seen by a camera on a public street.” In addition, cameras only take photographs or video when a vehicle has run a red light and, in most states, the camera does not photograph the driver or the occupants of the vehicle.

In most areas, red light enforcement cameras are installed and maintained by private firms. Lawsuits have been raised challenging private companies' rights to hand out citations, such as a December 2008 lawsuit challenging the city of Dallas' red light camera program, which was dismissed in March 2009. In most cases, citations are issued by law enforcement officers using the evidence provided by the companies.

There have been many instances where cities in the US have been found to have too-short yellow-light intervals at some intersections where red light cameras have been installed. In Tennessee, 176 drivers were refunded for fines paid after it was discovered that the length of the yellow was too short for that location, and motorists were caught running the light in the first second of the red phase. In California, a combined total of 7603 tickets were refunded or dismissed by the cities of Bakersfield, Costa Mesa, East LA, San Carlos, and Union City, because of too-short yellows. Although national guidelines addressing the length of traffic signals are available, traffic signal phase times are determined by the government employees of the city, county or state for that signalized location. While some states set jurisdiction-wide constant durations for yellow-light intervals, a new standard is taking hold. States are required to adopt the 2009 National Manual on Uniform Traffic Control Devices (MUTCD) as their legal state standard for traffic-control devices since 2011. These standards require engineering practices to be used to set yellow-light-timing durations at individual intersections and or corridors. For guidance to state authorities, MUTCD states yellow lights should have a minimum duration of 3 seconds and a maximum duration of 6 seconds. The deadline for compliance is 2014. In the US, if any part of a driver's vehicle has already passed into the intersection when the signal turns red, a violation is not generated. A ticket is only issued if the vehicle enters the intersection while the light is red.

In 2014, a bill was introduced in the United States House of Representatives attempting to prohibit red light cameras on federally funded highways and in the District of Columbia.