The Vienna Convention for the Protection of the Ozone Layer (1985) and its Montreal Protocol on Substances that Deplete the Ozone Layer (1987) are international agreements that were adopted to deal with the biggest environmental threat of the time: the discovery of a hole in the ozone layer.

The ozone layer is a region of high ozone concentration in the stratosphere, 20 to 30 kilometres above Earth's surface. It acts as an invisible shield and protects us, and all life on earth, from harmful ultraviolet (UV) radiation from the sun.

In the mid-1980s, scientists discovered a thinning in the ozone layer above Antarctica. Manmade chemicals containing halogens were determined to be the main cause of this ozone loss. These chemicals, collectively known as ozone-depleting substances (ODSs), include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons and methyl bromide. They were used in literally thousands of products, from air conditioners, refrigerators and aerosol cans, to solvents used to clean electronics, insulation foams, fire protection systems, inhalers and even shoe soles, as well as fumigants to kill pests.

Hailed as among the most successful such agreements in history, the ozone treaties bring together all the countries of the world, under a framework that gives them access to the latest scientific, environmental and technological information upon which to base their decisions. For more than 32 years the parties to the ozone treaties have worked together with the scientific world, the private sector and civil society to better understand the problem and to adopt and implement mechanisms to resolve it. As a result, the ozone layer is well on the road to recovery, but the continued commitment by all parties and all stakeholders is needed to ensure that the mission is accomplished.

The ozone treaties handbooks were created at the request of the Meeting of the Parties to the Montreal Protocol at its second meeting, in 1990, and have been updated after each yearly Meeting of the Parties to the Protocol (MOP) and three-yearly Conference of the Parties to the Convention (COP) since then. They consist of the treaty texts, as adjusted and amended over the years, along with all the decisions of the MOP and the COP, as well as relevant annexes and the rules of procedure. The handbooks comprise a record of the actions taken over more than three decades to protect the ozone layer. More than that, they are a crucial resource for the parties themselves, as well as the experts, industries, intergovernmental organizations and civil society groups that are involved in this important mission.