The Square Kilometre Array (SKA) is a proposed radio telescope which is intended to have a collecting area of approximately one square kilometre. It is planned to operate at frequencies of 0.10-25 GHz, with a goal of 0.06-35 GHz, and its size will make it 50 times more sensitive than current instruments. It may incorporate multiple independent fields of view, allowing several radio astronomers to observe at once, or to look at different areas of the sky simultaneously. The SKA will create images of distant radio sources using aperture synthesis. Construction of the SKA is scheduled to begin in 2011, with initial observations in 2014. It is intended to be fully operational by 2020. It will easily be the most sensitive radio instrument ever built, being able to detect every active galactic nucleus (AGN) out to a redshift of 6, when the universe was less than 1 billion years old. It will have the sensitivity to detect Earth-like radio leakage at a distance of several hundred to a few thousand light years.