Argentina and the UK have agreed to work toward removing measures restricting the oil and gas industry, shipping and fishing around the disputed Falkland Islands.
They also pledged to work together more closely on a range of bilateral issues including trade and security.
The islands, which Buenos Aires calls Las Malvinas, may also schedule more direct flights to Argentina.
The agreements would not affect the Falklands' sovereignty, the UK said.
This is the most positive development in relations between Argentina and Britain for more than 15 years, says the BBC's diplomatic correspondent Paul Adams.
Both Argentina and the UK claim the islands in the South Atlantic - with about 3,000 inhabitants - as their own, having fought a war over them in 1982.
'Open for business'
Wednesday's joint statement was agreed following a series of high-level meetings in Buenos Aires between Argentinian President Mauricio Macri and other senior officials, and UK Foreign Office minister Sir Alan Duncan.
Sir Alan said the Falkland Islands would be "free" to start more flights with layovers in Argentina. At present, there are occasional flights to Chile that stop in Argentina but this gives the green light to flights to other Latin American countries.
They also said they would support a project to try to identify the remains of unknown Argentines soldiers who died during the war and were buried on the islands.
The Foreign Office said it was the first positive statement the two sides had agreed on since 1999.
The UK's Sir Alan Duncan said: "It's clear to me that Argentina is open for business. The measures agreed today demonstrate we can make progress through dialogue."
Argentina's former president Cristina Fernandez de Kirchner pursued a claim of sovereignty over the islands and tried to put pressure on British and US companies not to drill for oil in the waters around them.
She required all vessels travelling between Argentina and the islands and those that wanted to cross Argentine territorial waters en route to the Falklands, to seek prior permission.
But her successor Mr Macri, who has been the president since December 2015, promised a "new kind of relationship" with the UK.
The Falklands are a UK overseas territory located about 530km (330 miles) off Argentina's coast.
In 2013 the islanders voted overwhelmingly to remain a UK territory.