The summary of the Senate Intelligence Committee report said the CIA misled Americans on the effectiveness of "enhanced interrogation".
It said interrogations were badly managed and the information collected unreliable.
President Obama previously said that in his view the techniques were torture.
The Senate committee's report runs to more than 6,000 pages, drawing on huge quantities of evidence, but it remains classified and only a 480-page summary is being released.
Publication had been delayed amid disagreements in Washington over what should be made public.
President Barack Obama halted the CIA interrogation programme when he took office in 2009.
Earlier this year he said that in his view the methods used to question al-Qaeda prisoners amounted to torture.