A panel marking the twinning of Plovdiv with Leningrad (now St. Petersburg) The project was by an author's team from St. Petersburg and was a composition of an allegorical figure, the names of the two cities in Cyrillic and the year of installation, written in Roman numerals - 1980 and affirms the brotherhood between the two socialist cities.

Plovdiv is one of the first cities to join the World Federation of Twin Cities. A Twinning was established at the City People's Council of Plovdiv, which was responsible for the twinning of Plovdiv with other second cities. During the period 1963-1968 Plovdiv twinned with Chisinau and Leningrad (St. Petersburg), Okayama and Thessaloniki. To date, Plovdiv has 29 twin cities.