In September 1987, 24 nations met to negotiate the final text and sign the Montreal Protocol on Substances that deplete the Ozone Layer (ODS). The agreed Montreal Protocol, which entered into force on January 1, 1989, limited production of most commonly used ODSs, i.e. chlorofluorocarbons (CFCs) and halons. The Protocol required each party's production of chlorofluorocarbons (CFC-11, 12, 112, 113, 114 and 115) first to be frozen at 1986 levels and ultimately reduced to 50% of 1986 levels by 1998. Production of halons 1211, 1301 and 2402 were to be restricted to 1986 levels. The Protocol called for a freeze in production of halons at 1986 levels beginning in 1992.

The London Amendment
Shortly after the 1987 Protocol was negotiated, new scientific evidence showed that ozone depletion was occurring at a rate significantly faster than previously assumed. Hence, in June 1990, the parties to the Protocol met in London and agreed to amendments that required more stringent controls on ODSs included in the original agreement. The London agreement added further controls on other important ODSs such as carbon tetrachloride (CTC) and 1,1,1-trichloroethane (1,1,1-TCE) also known as methyl chloroform (MC).

The London Amendment limited production of commonly used CFCs to 50 percent of 1986 levels by 1995 and 15% by 1997. Under the amended agreement, CFCs, halons and CTC production is to be phased out by the year 2000, and methyl chloroform is to be phased out by 2005. The 1990 amendment also introduced the concept of transitional substances, such as the HCFCs. These are envisaged to be chemical replacement for CFCs and other controlled substances and have relatively small ozone depletion potential. A non-binding resolution by the parties calls for a phase out of HCFCs by the year 2020, if possible, but not later than 2040. The London Amendment to the Protocol entered into force in August 1992.

The Copenhagen Amendment
Scientific data on depletion of the ozone layer presented to the Parties at their November meeting in Copenhagen revealed that depletion has been occurring at a rate twice as fast as originally observed. For example, at latitudes where 2% depletion had been observed over the last decade, new evidence showed that actual depletion is closer to 3 - 5%. The Copenhagen Amendment calls for an accelerated phase-out of ODS for the developed countries (CFCs, CTC, and, MC by 1996; HCFCs by 2030). Additionally, the Copenhagen Amendment calls for measures against hydrobromofluorocarbons (HBFCs) and methyl bromide. The Copenhagen Amendment to the Protocol was adopted in November 1992 to be effective from January 1, 1994, with ratification by at least twenty countries. As of May 1994, twenty-four countries have done so.

The developed country signatories of the Protocol are thus committed by the Copenhagen Amendment to a freeze of CFC production and consumption at 1986 levels from mid-1989 through 1993 followed by phased reductions of both production and consumption (defined as production plus imports minus export of bulk chemicals) leading to a complete phase-out of CFC and halons by 1996 (under November 1992 revised reduction schedule).

The Protocol grants a 10-year grace period on all phase out dates and interim reduction deadlines for developing countries whose per capital consumption of Annexure A chemicals is less than 0.3 kg/year. Annexure A chemicals include the five main CFCs: CFC-11, CFC-12, CFC-113, CFC-114, CFC-115; and halons. For most developing countries this allows some leeway to expand CFC consumption over the next several years. However, by the terms of the Protocol, such expansion is allowed only to "meet basic domestic needs". Production for export has been excluded from the definition of domestic needs.

The list of ODS that are regulated by the Montreal Protocol are thus: