The Thirty Meter Telescope has been in the works for nearly 20 years. The gigantic instrument (with a mirror nearly 100 feet across) promises to deliver new data about our Universe on an astronomical scale. Namely, it'll give us the ability to look farther back in time than we ever have before. 13 billion years, to be precise. With such a huge mirror, the Thirty Meter Telescope (or TMT for short) will be able to perceive light from the faintest, farthest, and oldest reaches of the known Universe.
Besides peering into the very beginnings of time, the Thirty Meter Telescope will also be used to search for dark matter and dark energy, figure out the relationship between supermassive black holes and their home galaxies, pick out each and every individual star in galaxies up to 30 million light years away (!), zoom in on exoplanets, and even provide new information about Kuiper belt objects (like comets) that live out around Pluto. That's some pretty amazing stuff.
The internationally-backed Thirty Meter Telescope hasn't been without its controversies, however. Despite the unique astronomical opportunity it affords us, it's the telescope's impact here on Earth that has drawn the most fire. Local groups have opposed the placement of the telescope at the Mauna Kea Observatories atop the volcano of the same name on the Big Island of Hawaii, and environmental and cultural complaints have been in process since 2011. But in February that all came to an end, and the Thirty Meter Telescope is slated to break ground next April. We should be seeing the first images from the TMT in 2018.