The new inquests into Britain's worst sporting disaster were ordered in December 2012 when the High Court quashed accidental death verdicts from 21 years ago after an independent inquiry found new evidence and absolved the fans of any responsibility.
Ninety-six Liverpool F.C. supporters died and another 766 people were injured after a crush in an enclosed, overcrowded terrace at the stadium in the northern city of Sheffield on April 15, 1989, during an FA Cup semi-final against Nottingham Forest.
The new hearing before a jury is expected to hear evidence on issues such as stadium safety, emergency planning, crowd management and the response of the emergency services.
Relatives said they were relieved the day had arrived after fighting for years for "Justice for the 96", refusing to accept the deaths were accidental and accusing police of covering up exactly what happened.
"I'm really, really nervous. It's been a long, long figh... but this is the beginning now, hopefully it can be put right," Charlotte Hennessy, who lost her father James in the disaster when she was six, told Britain's Press Association.
The tragedy which happened within minutes of kick-off shocked the world and led to a new era of modern stadiums across Britain. Banks of terracing and metal fences around pitches disappeared, replaced by seating and better security.
The new inquests, to be held at Warrington in northern England, are expected to last for months with no verdicts handed down until 2015 due to the amount of paperwork to be examined.
The disaster is also the subject of two other investigations.
The government in 2012 set up a new police investigation into the Hillsborough disaster in a victory for victims' families who never accepted the official version of events.
The Independent Police Complaints Commission is also looking into allegations arising from the aftermath of the tragedy and will review allegations surrounding amendments to statements and the actions of police officers.
Next month, on the 25th anniversary of the disaster, matches in England will kick off seven minutes late as a mark of respect.