The American soldier accused of the biggest leak of classified information in US history, which prosecutors say put lives at risk, is going on trial in a case that raises questions about the limits of secrecy and openness in the internet era.
Private First Class Bradley Manning, 25, is charged with providing more than 700,000 documents to WikiLeaks, an anti-secrecy website.
He said the move was intended to prompt renewed debate on US military action. But the government says the leaks damaged national security and endangered American lives. He faces a possible life sentence if convicted.
The military trial at Fort Meade, Maryland, about 50km northeast of Washington, is expected to run from Monday until at least late August. Prosecutors have said they expect to call more than 100 witnesses.
Civil liberties groups say the court-martial has been shrouded in secrecy and has had a chilling effect on whistleblowers.
Manning faces 21 counts, including the most serious one of aiding the enemy, as well as prosecution under the Espionage Act of 1917.
Manning, an intelligence analyst, was arrested in May 2010 while serving in Iraq. He was charged with downloading intelligence documents, diplomatic cables and combat videos and forwarding them to WikiLeaks, which began releasing the information that year.
Manning testified in February that he had released the files to spark a domestic debate on the military and on foreign policy in general.
"I take full responsibility for my actions," he said at the time. "I felt I accomplished something that would allow me to have a clear conscience."