Joint Or Multiple Country Issues

France - Portugal Joint Issue
Capitals
October 21, 2016
The stamp sets feature Rua Augusta Arch (Lisbon) and Rue Royale (Paris).
(designed and engraved by Yves Beaujard)

Czech republic - Liechtenstein Joint Issue
Young Woman on a Balcony by Gerrit Dou
September 5, 2016 (Liechtenstein)
September 7, 2016 (Czech Republic)
Gerrit Dou (1613 – 1675 was a Dutch Golden Age painter. He was a student of Rembrandt. He specialized in interiors and niche paintings and is noted for his strong chiaroscuro technique.
Young Woman on a Balcony is one of the works of art donated by Johann II of Liechtenstein to the predecessor of today's National Gallery of Prague.

Mexico - Jamaica Joint Issue
The 50th anniversary of the Diplomatic Relations
October 28, 2016
The stamps showcase Jamaican giant swallowtail (Papilio homerus) and Monarch butterfly (Danaus plexippus).

How about the US/Canada St Lawrence Seaway stamp?

Jack Kelley

Italy - San Marino Joint Issue
9th Centenary of the Dedication of St Mark's Basilica
October 8, 1994
The St Mark's Basilica is the Patriarchal Cathedral of the Roman Catholic Archdiocese of Venice. The present Basilica, the third one, was built with a mixture of Italian and Byzantine features around the second half of the XI century.

Vatican - Spain Joint Issue
World Youth Day 2011 Madrid
July 1, 2011
World Youth Day 2011 was a Catholic event held from August 16 to 21 in Madrid.

Ireland - Spain Joint Issue
Popular Dances
November 7, 2008
The souvenir sheet features Flamenco and Irish stepdance.

France - Switzerland Joint Issue
Modern Art
November 25, 1988 (Switzerland)
November 26, 1988 (France)
Métamécanique by Jean Tinguely (1925 - 1991)

Portugal - Peru Joint Issue
Raul Maria Pereira
August 10, 2007
The joint issue honors Raul Maria Pereira (1877 - 1933), a Portuguese painter, architect and diplomat. He spent the last years of his life in Lima, Peru.

France - Romania Joint Issue
Constantin Brâncusi
September 25, 2006 (Romania)
September 26, 2006 (France)
The joint issue honors Constantin Brâncusi (1876-1957), one of the most influential sculptors of the 20th-century. The designs feature his work Sleeping Muse and Sleep.

France - Denmark Joint Issue
Danish - French Culture Year
September 22, 1988 (Denmark)
September 26, 1988 (France)
The stamps feature a modern sculpture Homage to Leon Degand by Robert Jacobsen (1912 - 1993).
(engraver: Pierre Forget)

Australia - Germany Joint Issue
Bicentenary of Ludwig Leichhardt
October 10, 2013 (Germany)
October 15, 2013 (Australia)
The stamps commemorate Ludwig Leichhardt, (1813 – ca. 1848), a Prussian explorer and naturalist, most famous for his exploration of northern and central Australia. He and his team disappeared during an expedition in 1848.

300th Anniversary of the Birth of Maria Theresa - Joint Issue between Austria, Croatia, Hungary and Slovenia.

Ukraine - Bulgaria Joint Issue
Black Sea Fauna and Flora
May 22, 2017
The souvenir sheets feature Black Sea Dolphin (Delphinus delphis ponticus) and Marine Bivalve Mollusk (Barnea candida).

Slovakia - Serbia Joint Issue
Ján Koniarek
April 12, 2012 (Serbia)
April 13, 2012 (Slovakia)
Ján Koniarek (1878 - 1952) was a Slovak sculptor, one of the founders of modern Slovak sculpture. He was in Serbia (Belgrade) between 1906 and 1914 and was a soldier in WWI.
The joint issue features his bronze sculpture John the Baptist (1906).