Lord Justice Leveson also revealed plans to invite all newspaper editors, journalists and media owners to disclose what they see as "inappropriate" practices in the industry.
The inquiry, announced by Prime Minister David Cameron last month, will examine the ethics of the press and its relationship with the public, politicians and police. Public hearings will start in September, due to report back within a year.
The process follows a flood of allegations of widespread phone hacking at the News of the World, prompting News International to shut down the Sunday tabloid earlier this month.
Lord Leveson called on the newspaper and media industries not to "close ranks" and allow him to discover the true scale of the use of phone hacking and other illegal practices.
"It may be tempting for a number of people to close ranks and suggest the problem is or was local to a small group of journalists then operating at the News of the World," he said.
"I would encourage all to take a wider picture of the public good, and help me grapple with the length, width and depth of the problem as it exists."
Last week, it was reported that Leveson had attended functions with Rupert Murdoch's son-in-law, but he said today that he would not have accepted the role if he had "the slightest doubt" about his suitability.
Rupert Murdoch, his son James and former News International chief executive Rebekah Brooks were questioned last week by MPs on the culture, media and sport select committee.
However, News International chairman James Murdoch is facing a parliamentary inquiry into whether he gave misleading evidence to MPs on the committee over a key email potentially showing that knowledge of phone hacking went beyond "one rogue reporter". Two former News International executives have said that Murdoch was "mistaken" in his statements given last Tuesday.
Lord Leveson said that there "needs to be a discussion" at some point about what amounts to the public good in news reporting, and "to what extent the public interest should be taken into account and by whom".
Meanwhile, the home affairs select committee has ordered one of News International's main technology contractors to answer questions on its knowledge of the alleged deletion of emails by the newspaper publisher.
Keith Vaz, the committee chairman, has sent a letter to HCL Technologies, following allegations that the India-based firm knew about the destruction of emails potentially revealing the scale of phone hacking at News International.
Yesterday, Piers Morgan was forced to deny fresh allegations threatening to link him to the phone hacking scandal while he was editor of The Mirror.