The Extremely Large Telescope (ELT) will be the world's largest telescope seeing visible and infra-red wavelengths. It is currently under construction, and is due to be completed in 2024. The primary mirror is 40 metres in diameter, and will collect 100 million times more light than the human eye.

Since 2000, the National Astronomical Observatory of Japan (NAOJ) has been operating one of the largest and most sophisticated telescopes in the world at the summit of Mauna Kea in Hawaii. The Subaru telescope saw first-light (i.e. started observing) early in 1999 and is currently conducting routine research. Along with other observatories around the world, is making many important discoveries about the Universe we live in.

The 6.5 metre Multiple Mirror Telescope (MMT) is a joint venture between the Smithsonian Institution and the University of Arizona. The MMT is located on the summit of Mt. Hopkins, the second highest peak in the Santa Rita Range, approximately 55 kilometres (30 miles) south of Tucson, Arizona.

The William Herschel Telescope (WHT) is the largest UK owned telescope in the Canary Isles, and indeed throughout the northern hemisphere. It was built during the 1980's and first saw operation in 1987.

At 11 metres in diameter, the Southern Africa Large Telescope (SALT) is the largest single optical telescope in the southern hemisphere, able to detect stars one billion times dimmer than the faintest visible to the unaided eye. It is sited at the Southern Africa Observatory site near Sutherland, Northern Cape.

The main mirror, however, is not one single piece of glass, but made up of 91 hexagonal mirror segments which are all carefully joined and aligned to reflect the light as if they were one mirror.