在一个企业中，有几个因素会影响那些不直接参与个人，公司或家庭的消费生产和投资决策的人。间接影响可能微不足道或可能干扰消费和生产。这些被经济学家称为外部性。它可以是生产或消费的成本或收益，但不影响生产者或消费者，而是落在不参与生产或消费的人身上。 （McTaggart.D. Findlay.C.Parkin.M Economics）。由于间接影响并不影响定价，而只影响他人的消费和生产机会，因此私人收益与公共收益之间存在差异。外部性可能是负面的或正面的。政府对经济领域的干预是由于外部性的盛行。有两种外部性：负面和正面的外部性。负外部性使得外部成本和正外部性成为外部效益。
In a business there are several factors which affect people who are not directly involved in the consumption production and investment decisions of individuals, firms or household. The indirect effects may be insignificant or can be interfering in the consumption and production. These are called as externalities by the economists. It can be a cost or a benefit from production or consumption but does not affect the producer or the consumer instead falls on someone who is not involved in production or consumption. (McTaggart.D. Findlay.C. Parkin.M Economics). As the indirect effect does not have an impact on the pricing but only on the consumption and production opportunities of others, there is a difference between private returns and public returns. Externality may be negative or positive. The need for government interference in the economic sphere is due to the prevalence of externalities. There are two types of externalities: negative and positive externality. A negative externality imposes external cost and positive externality an external benefit.
Imposing external cost on third parties who are not in the market and not paying appropriate compensation is referred as negative externality. This includes negative production externalities and negative consumption externalities. In the day to day life, many examples of negative consumption externalities can be noticed. For example smoking, noisy crowd, etc. Examples for negative production externality are pollution, noise from aircraft etc. The external cost of public litter cleaning is also an example. The economics of negative consumption externality can be put in economic terms as private marginal cost (PMC) and social marginal cost (SMC) (Krabbe et al, 1992).