The twinning of cities is not a new concept for human society. For years, there have been partnerships that date back to Europe in the second century. These links were limited to cities and municipalities (local authorities) in the early years. Since then, links have been established between schools, churches, libraries, port authorities, airports, radio and television stations, postal services and other local authorities, and charities, regional, regional and provincial governments. Twinning agreements are legal or social agreements between two cities to promote trade and tourism. Institutions, organizations and governments at the second and third levels are committed to participating in joint exchanges and activities to enrich partners. The goal is to find strength in their unity. For a long time, twinning was considered a sterile activity. This idea is now considered superfluous, given that, since the Second World War, partnership agreements for the promotion of peace and cultural exchanges have multiplied and some worthy successes have been achieved.
According to a McKinsey study, one-third of the world`s GDP will come from only 100 cities. At the heart of this change is globalization, which strengthens trade flows between regions and shifts economic power to the emerging economies of China and India or the cities of those regions. ”It`s cities, not nations, that fuel the global economy and drive growth through productivity, innovation and job creation,” says David Adam, founder of Global Cities, which advises cities on positioning, branding and investment opportunities. It is therefore important for leaders to understand how global economic factors can influence the competitiveness of their city/region and to determine how their unique assets can cope with the effects of globalization, so that they can benefit from new trade flows, direct investment, job creation and innovation, and remain an attractive offer in a global economy. This involves the search for a strategic partnership with a ”sister city” that allows the exchange of knowledge and ideas on different topics. Partnering with a city with experience in certain businesses solves the problems of the new partner city. Investments can be accelerated, as there are direct links between the chambers of commerce of the two municipalities of the territory. City twinning begins for many reasons. In general, twin cities have similar demographics and sizes. They can be created from business links, travel, similar industries, diaspora communities or common history. This is how the partnership between Portland, Oregon and Bologna, Italy, was born of common industries in the field of biotechnology and education and a ”similar attitude towards food”, while Chicago`s link with Warsaw, Poland, with the historic Polish community of Chicago began.  The twinning between Indianapolis and Monza, Italy, is due to the long connection between the two cities and motor racing.
China`s relations are managed by the Chinese People`s Association for Friendship with Foreigners.  City twinning is supported in Japan by the Council of Local Authorities for International Relations, a joint agency of local governments established by the Japanese government in 1988 (like Sister Cities International, its equivalent in the United States). More recently, at the initiative of its governor Yoichi Masuzoe, Tokyo has begun to actively promote ”urban diplomacy” with other cities.  Although not legally binding, signing a formal partnership ”sworn” or agreement facilitates the establishment of a long-term relationship of trust. Its form and content are not defined and can be modified according to the type of partnership established and the will of the twin cities. Choosing the right partnership requires a detailed analysis of the market, in conjunction with urban information, in order to identify the potential for synergies between two cities/regions. Some of the similarities