Guernsey and Jersey's governments have renewed their partnership with the French department Ille-et-Vilaine.
The Memorandum of Understanding facilitates joint working in areas such as education, overseas aid and trade.
The Channel Islands also signed a memorandum with the region of Brittany for the first time.
The President of the regional council of Brittany, Loïg Chesnais-Girard, said the agreement would strengthen its relationship with the islands.
He said: "While Brexit could have divided us, it has instead helped to bring the Channel Islands closer to Brittany and Normandy.
"I thank our partners in Jersey and Guernsey for having favoured the path of dialogue and cooperation, I am convinced that this path will best defend the interest of all our citizens."
The annual political summit, hosted in Guernsey, covered "many regional issues", and enabled "discussions with regional partners on strategic issues".
These included broader political relationships and areas of mutual interest within Europe and the European Union.
Guernsey and Jersey's governments said the new memorandum with Brittany would open discussion on economic development issues, maritime links and their relationships between the ports.
Member of the Policy and Resources Committee, Deputy Jonathan Le Tocq, said it would "enable us to deepen the connections that we have with the whole of this significant region to the south of us".
"In the French political system regions have different mandates and responsibilities to departments and so this new partnership will enable us to focus on new areas as well as build on our existing links, working with some of our closest neighbours," he said.
Deputy Philip Ozouf, Minister for External Relations, said the renewal of the partnership with Ille-et-Vilaine for another three years showed its "close and productive relationship".
He said: "The fact that we are renewing our partnership is testimony to the enduring nature of our links and I look forward to working together on projects over the next three years.
"I wish to ensure the strengthening of these close and sharing ties that contribute to the enrichment of our respective jurisdictions over the long term."
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