Green computing, green IT (Information Technology), or Information and Communication Technology Sustainability, is the study and practice of environmentally sustainable computing or IT.

The goals of green computing include optimising energy efficiency during the product's lifecycle; leveraging greener energy sources to power the product and its network; improving the reusability, maintainability, and repairability of the product to extend its lifecycle; improving the recyclability or biodegradability of e-waste to support circular economy ambitions; and aligning the manufacture and use of IT systems with environmental and social goals. Green computing is important for all classes of systems, ranging from handheld systems to large-scale data centers.

Sustainable development is a concept that redefines the notion of the general interest by integrating environmental, social, and economic considerations. Many corporate IT departments have green computing initiatives to reduce the environmental effect of their IT operations. Yet it is also clear that the environmental footprint of the sector is significant, estimated at 5-9% of the world's total electricity use and more than 2% of all emissions. Data centers and telecommunications networks will need to become more energy efficient, reuse waste energy, use more renewable energy sources, and use less water for cooling to stay competitive. Some believe they can and should become climate neutral by 2030 ^{[citation needed]}

The carbon emissions associated with manufacturing devices and network infrastructures is also a key factor.

Green computing can involve complex trade-offs. It can be useful to distinguish between IT for environmental sustainability and the environmental sustainability of IT. Although green IT focuses on the environmental sustainability of IT, in practice these two aspects are often interconnected. For example, launching an online shopping platform may increase the carbon footprint of a company's own IT operations, while at the same time helping customers to purchase products remotely, without requiring them to drive, in turn reducing greenhouse gas emission related to travel. The company might be able to take credit for these decarbonisation benefits under its Scope 3 emissions reporting, which includes emissions from across the entire value chain.

In 1992, the U.S. Environmental Protection Agency launched Energy Star, a voluntary labeling program that is designed to promote and recognize the energy efficiency in monitors, climate control equipment, and other technologies. This resulted in the widespread adoption of sleep mode among consumer electronics. Concurrently, the Swedish organization TCO Development launched the TCO Certified program to promote low magnetic and electrical emissions from CRT-based computer displays; this program was later expanded to include criteria on energy consumption, ergonomics, and the use of hazardous materials in construction.

In 2009 the Organisation for Economic Co-operation and Development (OECD) published a survey of over 90 government and industry initiatives on "Green ICTs" (Information and Communication Technologies), the environment and climate change. The report concluded that initiatives tended to concentrate on the greening ICTs themselves, rather than on their actual implementation to reduce global warming and environmental degradation. In general, only 20% of initiatives had measurable targets, with government programs tending to include targets more frequently than business associations.

Many governmental agencies have continued to implement standards and regulations that encourage green computing. The Energy Star program was revised in October 2006 to include stricter efficiency requirements for computer equipment, along with a tiered ranking system for approved products.