The foundations for Bonn's development as Germany’s United Nations City were laid on 20 June 1996 - exactly five years after the Bonn-Berlin resolution of the German Federal Parliament.

In the presence of the then Federal Environment Minister Angela Merkel and former UN Secretary-General Boutros Boutros-Ghali, the United Nations flag was hoisted in front of House Carstanjen. The United Nations Volunteers Secretariat (UNV) had just moved in there; the Climate Change Secretariat (UNFCCC) followed shortly afterwards.

Today, around 20 United Nations organizations with around 1,000 employees and more than 150 national and international non-governmental organizations are based in Bonn.

As early as 1951, the United Nations High Commissioner for Refugees (UNHCR) opened a liaison office in the then federal capital Bonn, and in 1953 an office of the International Labour Organization (ILO) was established in the city.

The Convention on the Conservation of Migratory Species of Wild Animals was adopted at Godesburg castle in 1979. The "Bonn Convention" opened its doors in 1984 as the first independent UN agency in Bonn and is still based here today.

The Bonn-Berlin Resolution of 20 June 1991 set a new target for Bonn by laying down "the assumption and relocation of new functions and institutions of national and international importance". With the Berlin/Bonn Law and a compensation agreement, Bonn was able to create the infrastructures corresponding to this role, above all the spatial conditions for the future work of multilateral institutions.

The first new organization the United Nations relocated from Geneva to Bonn was the United Nations Volunteers (UNV) programme. At the same time, the Federal Government was awarded the mandate for the establishment of the new Climate Secretariat at the 1995 Climate Summit in Berlin. The first building to be handed over to the United Nations in Bonn was a building of historic importance: the idyllic „Haus Carstanjen“ on the Rhine was the place where the Marshall Plan was adopted and signed after the Second World War. In 1996 UNV, UNFCCC and UNIC moved into Haus Carstanjen on the river banks.

In 1998, the Bonn Convention is given a new generation - two regional agreements are settled in Bonn: the Secretariat of the Agreement on the Conservation of Small Cetaceans of the North and Baltic Seas (ASCOBANS) and the Agreement on the Conservation of European Bat Populations (EUROBATS).

A highlight of the first decade of settlement was certainly the arrival of the Secretariat of the Convention to Combat Desertification (UNCCD). Already at this time, Bonn could refer to a network of institutions which, as a result of the Rio Conference in 1992, dealt with issues of sustainability and thus the sustainability of our planet.

And year after year new agencies were added, mostly small but constantly growing.

A further milestone in the development of Bonn as a UN location is reached on 11 July 2006: The Federal Government makes available to the United Nations the former high-rise parliament building, also known as the „Langer Eugen“. Kofi Annan and Chancellor Angela Merkel ceremoniously open the new office. The UN Secretary-General emphasized at the ceremony that the great hospitality UN Bonn was receiving in the city had made Bonn one of the most attractive and rewarding places to work for the United Nations. And the Federal Chancellor added: "It is the explicit wish of the entire Federal Government to see the UN host city Bonn develop further, with a special focus on environment and development".

The UN Tower is the heart of the UN Campus. In the immediate vicinity is the UNFCCC headquarters in the Old Parliament Building. The building was refurbished as an ecological model building. The Waterworks and Pump House were also added to the UN Campus to give the Bonn-based agencies space for smaller conferences. House Carstanjen is still in use and another building is already under construction.

The 20-year history of the UN Bonn is a success story, indeed! The City of Bonn celebrated its 20th anniversary as Germany’s United Nations City with a diverse calendar of public and professional events from April to November 2016. And Bonn’s citizens celebrated with great enthusiasm. In June 2016, for example, 10,000 visitors flocked to the Citizens' Festival at Villa Hammerschmidt and the Federal Ministry for Economic Cooperation and Development (BMZ).

The UN city has long since become a recognized international location: More than 150 non-governmental organizations operate from here and are also mostly active in the field of sustainability. A special focal point and hub for sustainability developed with the adoption of Agenda 2030 in September 2015. Bonn is now not only home to the Global Action Campaign for the 17 Sustainable Development Goals (SDGs), but also to a Knowledge Centre for Sustainable Development of the United Nations Staff College. Institutions from science and research and global business players round off the picture.

The employees of the UN in Bonn agree with their former boss Kofi Annan: "Bonn is so romantic, so familiar and so safe" can be heard time and again.

A city that is host to the United Nations needs a suitable conference infrastructure, even for the large Conferences of the Parties. With the Bellevue Treaty, signed on 27 February 2002, the expansion of the World Conference Center Bonn begins. In the presence of UN Secretary-General Kofi Annan and Federal President Johannes Rau, the Federal Government, the State of North Rhine-Westphalia and the City of Bonn sign the agreement on the establishment of international institutions in Bonn and on the conference center.

Meetings and conferences of the United Nations have become an important feature of Bonn. Peace, voluntary commitment, species protection, early warning of catastrophes, combating land degradation and climate protection are just some of the topics that the United Nations are dealing with from Bonn. By far the largest volume of meetings is provided by the Climate Secretariat (UNFCCC) - three Conferences of the Parties have taken place in Bonn, most recently with more than 22,000 participants in autumn 2017.