The 11 charges against him include murder, rape, enslavement and conscripting child soldiers.
Taylor, the first former African head of state to appear before an international tribunal, has pleaded not guilty to all charges.
Prosecutors say Taylor's desire to get his hands on diamonds from Sierra Leone was one of the root causes of his alleged involvement in that country's civil war.
Their first witness to appear on Monday will be Ian Smillie, an expert on conflict and blood diamonds - so called because the proceeds from their illegal sales have been used to fund wars across Africa since the 1990s.
Smillie is the first of 144 prosecution witnesses, though trial attorneys expect only half of them to appear in person. The complex case will likely last nearly two years.
The second witness scheduled to testify was a victim of the militias.
Taylor's defence team does not deny atrocities happened in Sierra Leone, and has argued that calling victims is an unnecessary appeal to the emotions of the judges.
But Stephen Rapp, the chief prosecutor at the UN-backed Special Court for Sierra Leone, said he had an obligation to highlight the suffering of the victims.
"We owe it to the victims to present some testimony in a live sense," Rapp said, so as "not to drain the case of the human element completely".
Later in the week, a former member of Taylor's inner circle will testify about how the former Liberian president allegedly controlled and encouraged militias in neighbouring Sierra Leone.
Nearly 60 witnesses will be called to draw links between Taylor and the militias, and most are expected to do so anonymously for fear of reprisals by Taylor's supporters.
The trial is being held in The Hague for fear that staging it in the Sierra Leone capital, Freetown, could spark fresh unrest there. However, the courtroom action is being beamed to Freetown and members of the public have been invited to watch at the court's headquarters.
Monday's resumption comes six months after Taylor boycotted the start of his trial, claiming he would not be given a fair hearing, and fired his attorney. He has since appointed a new team led by Courtenay Griffiths, an experienced British lawyer.