A proactive method of dealing with the environment based on the idea that if the costs of current activities are uncertain but are potentially both high and irreversible then society should take action before the uncertainty is resolved. The Convention for the Prevention of Marine Pollution by Dumping from Ships and Aircraft (Oslo Convention) (1972) is an early example of the use of the precautionary principle since this convention, and subsequent ones, used a system of ‘black’ and ‘grey’ lists covering substances that could not be disposed of at sea and those for which a licence was required. Substances could be placed on the black list even if scientific evidence of harm was not fully available, so that discharges did not continue just because there was no proof of environmental damage. The Vienna Convention for the Protection of the Ozone Layer (1985) and Montreal Protocol (1987) were at the time quite unique amongst international environmental initiatives, because it was probably the first time that serious attempts were made to avert a major environmental problem before the more serious consequences and side‐ effects were obvious. Previously governments would have insisted on waiting for conclusive scientific proof of cause–effect links before introducing appropriate preventive legislation and embarking on costly behaviour‐changing strategies. Also known as the do‐no‐harm principle. Contrast wait‐and‐see principle. See also no regrets policy.