A federal judge in New York has allowed lawsuits over the 11 September attacks to proceed against the operators of the World Trade Center.
Litigation has been initiated by about 70 people who were either injured in the attacks in New York, Washington DC, and Pennsylvania, or whose relatives died.
Defendants include the Port Authority of New York and New Jersey, which owned the World Trade Center.
The defendants argue that they should not be held liable because the suicide attacks were unprecedented and impossible to guard against.
More to come?
The BBC's Jane Standley in New York says court officials are now preparing for a possible deluge of cases in the coming weeks, as people bereaved on 11 September choose lawsuits over government compensation.
They have until the end of the year to accept guaranteed government money for their injuries or loss - but in return they must give up their right to sue.
Less than half of those entitled have stated an interest in applying to the government fund.
Many have instead been waiting for this court ruling, our correspondent says.
More than 3,000 people were killed in the airline attacks on New York's Twin Towers and the Pentagon, and in the crash of a fourth hijacked plane in Pennsylvania.
Logically the solution is to sue the people who own the World Trade Center, since it is entirely due to their negligence that people died. "Had the twin towers of the World Trade Center been constructed to be invincible" suggested one claimant, "this would never have been allowed to happen, and my baby would still have a daddy!"