Tsarnaev faces 30 terrorism charges and prosecutors have asked for the death penalty if he is convicted. A jury would first need to vote to convict him and then vote a second time on whether to impose the death penalty.His lawyers have offered to have him plead guilty if prosecutors drop their demand for the death sentence but so far the US government has refused to make a deal.
Although the trial starts today it will be weeks before the prosecution and defence actually begin making their cases. The first step is to find 12 men and women who can sit on the jury and be trusted to give an impartial verdict.
Around 1,200 potential jurors will report to the court today and the judge and lawyers will begin the process of whittling them down to just a dozen. Anyone with a close connection to someone caught up in the bombing will be ruled out, as will anyone who says they would never to vote to impose the death penalty.
Jury selection is expected to take around a month and the overall trial is expected to take around four months.
Tsarnaev is being defended by Judy Clarke, a specialist in high-profile death penalty cases. She previously defended the Unabomber, a recluse who engaged in a two-decade bombing campaign across the US, and a man who in 2011 shot Congresswoman Gabby Giffords and killed six other people.
Ms Clarke has tried to delay the trial and have it moved outside of Boston, arguing that it will be impossible to assemble an impartial jury so close to the scene of the crime. Both of her efforts have been denied.