Eigg (; Scottish Gaelic: Eige; Scots: Eigg) is one of the Small Isles in the Scottish Inner Hebrides. It lies to the south of the Isle of Skye and to the north of the Ardnamurchan peninsula. Eigg is 9 kilometres (5+1⁄2 miles) long from north to south, and 5 km (3 mi) east to west. With an area of 12 sq mi (31 km²), it is the second-largest of the Small Isles after Rùm. Eigg generates virtually all of its electricity using renewable energy.

Eigg has been owned by the Isle of Eigg Heritage Trust since 1997, as a community ownership; another stakeholder, the Scottish Wildlife Trust, manages the island as a nature reserve. In April 2019, National Geographic discussed the island in an online article, estimating the population at 107 and the average number of annual visitors at 10,000.

The Heritage Trust provisioned a mains electricity grid, powered from near 100% renewable energy sources. Previously, the island was not served by mains electricity and individual crofthouses had wind, hydro or diesel generators and the aim of the project is to develop an electricity supply that is environmentally and economically sustainable.

The new system incorporates a 9.9 kWp PV system, three hydro generation systems (totalling 112 kW) and a 24 kW wind farm supported by stand-by diesel generation, ultra-capacitors, flywheels and batteries to guarantee continuous availability of power. A load management system has been installed to provide optimal use of the renewables. This combination of solar, wind and hydro power should provide a network that is self-sufficient and powered 98 percent from renewable sources. On 1 February 2008 the system was switched on.

Eigg Electric generates a finite amount of energy and so Eigg residents agreed from the outset to cap electricity use at 5 kW at any one time for households, and 10 kW for businesses. If renewable resources are low, for example when there is less rain or wind, a "traffic light" system asks residents to keep their usage to a minimum. The traffic light reduces demand by up to 20 percent and ensures that there's always enough energy for everyone.

The Heritage Trust has formed a company, Eigg Electric Ltd, to operate the new £1.6 million network, which has been part funded by the National Lottery and the Highlands and Islands Community Energy Company.

In September 2008, Eigg began a year-long series of projects as part of their success as one of ten finalists in NESTA's Big Green Challenge. While the challenge finished in September 2009, the work to make the island "green" is continuing with solar water panels, alternative fuels, mass domestic insulation, transport and local food all being tackled. In May 2009, the island hosted the "Giant's Footstep Family Festival", which included talks, workshops, music, theatre and advice about what individuals and communities can do to tackle climate change.

In January 2010, Eigg was announced as one of three joint winners in NESTA's Big Green Challenge, winning a prize of £300,000. Eigg also won the prestigious UK Gold Award in July 2010.