Décines has established two twin-city relations.
The first twin-city agreement was signed on 11 April 1992, with the Armenian city of Stepanavan. Located 140 kilometres north of Erevan and 120 kilometres south of Tbilissi (Republic of Georgia), Stepanavan was struck by a severe earthquake on 7 December 1988, leaving hundreds of victims and thousands without shelter.

Décines' second twin-city agreement was signed on 6 October 2001 with the Italian city of Monsummano Terme, in the Tuscany region, 50 kilometres from Pisa and Florence. Famed for its thermal baths, as well as for its important industrial activity, Monsummano Terme is also the birthplace of French actor and singer Yves Montand.

These two twin-city agreements have generated a great number of exchanges, in particular in the area of culture and sports, as well as joint actions involving youth. The Twinning Committee of Décines, established in 1993, takes an active part in the developement of strong ties between Décines and its twin cities.

On 9 November 2002, on the occasion of the 10th anniversary of the Décines-Stepanavan twinning, Décines, Stepanavan and Monsummano Terme signed a declaration of intention expressing their commitment to pursue a Tri-City partnership.