The man leading the judicial inquiry into phone hacking pledged to carry it out in a "spirit of complete transparency" as he urged media bosses to volunteer examples of "inappropriate" practices.
Lord Justice Leveson sought to quash questions over his impartiality after it emerged he had social connections with the Murdoch family.
He said it was "inevitable" that there would be some contacts between the inquiry panel and the organisations that would be under investigation but he was satisfied there were no conflicts of interest.
Each panel member provided a declaration of interests that were "the best of our recollection and provided in the spirit of complete transparency, which I intend should be one of the principal objectives of all of our work", he added.
Lord Justice Leveson was speaking as the panel met in Westminster to outline the procedures and time-scale for the first section of the probe.
That will investigate the culture, practices and ethics of the press and will initially focus on the relationship between the public and the media. The spotlight will be turned on links between the media, police and politicians in "due course".
Lord Justice Leveson advised editors and journalists to co-operate voluntarily with the inquiry and urged them not to "close ranks".
He will use his powers to demand evidence is handed over as soon as possible.
He said: "At some stage, there needs to be a discussion of what amounts to the public good, to what extent the public interest should be taken into account and by whom."
He added: "I could, of course, require journalists to provide me with their files of examples for they are indeed essential to provide a factual background to the important issues that we must discuss but, at this stage, I would rather invite editors, proprietors of magazines and journalists to assist me by providing a wide range of examples of what is contended to be inappropriate for one reason or another across the fullest range of titles.
"It may be tempting for a number of people to close ranks and suggest that the problem is or was local to a group of journalists then operating at the News of the World, but I would encourage all to take a wider view of the public good and help me grapple with the width and depth of the problem."
The first public hearings in the phone-hacking inquiry will be held in September but Lord Justice Leveson indicated the panel could miss the 12-month deadline for producing the first report because the terms of reference "grew very substantially" after the Prime Minister's initial statement announcing a probe.
He said he would "strive" to meet that deadline, but "not at all costs".
All witnesses will give evidence under oath and some will receive legal letters ordering them to appear.
The notices will be sent out in "waves" but "no discourtesy is intended" and "no conclusions should be drawn", the inquiry judge insisted.
The second section of the inquiry will look at the specific phone-hacking allegations that arose in the wake of the scandal at the News of the World but will only begin once police investigations have been completed.
Lord Justice Leveson, 62, prosecuted serial killer Rose West, and was the senior presiding judge in England and Wales between 2006 and 2009.
He is heading a panel of experts from the legal, media, political and policing professions.
David Cameron established the investigation under the Inquiries Act 2005, giving it powers to summon witnesses, including newspaper reporters, management, proprietors, policemen and politicians of all parties.