The BBC Trust and the S4C Authority today (August 10) launched a public consultation on the Operating Agreement, which sets out the new relationship once the majority of S4C's funding comes from the BBC licence fee from April 2013.
This shift was initially agreed in October 2010, when the BBC reached a new licence fee settlement with culture secretary Jeremy Hunt, involving big spending cuts and various new funding responsibilities, including S4C.
Individuals and groups have ten weeks to October 23 to state their views on the draft operating agreement, which aims to "ensure the editorial and managerial independence of the S4C service".
In October 2011, the BBC and S4C reached the deal after finding a compromise that would protect S4C's independence, while also allowing the BBC Trust to keep it accountable for all licence fee cash spent.
The BBC National Trustee for Wales, Prof Elan Closs Stephens, said that the corporation wants to bring the best value for Welsh-speaking audiences.
"My main priority is to help S4C to provide the best possible programmes for Welsh speaking audiences, while safeguarding S4C's editorial independence and ensuring that licence fee money is spent wisely", he said.
"This new agreement between the BBC and S4C builds on the last 30 years of a successful partnership between us."
Huw Jones, the chair of the S4C Authority, added: "I believe that the Operating Agreement provides reassurance that S4C's future and its ability to act independently have been secured, while ensuring appropriate accountability to the BBC Trust for use of the licence fee."
Anyone wishing to make submissions to the consultation can find more details here.