Wikimedia
Wikipedia: Externality
Provides a definition and examples of an externality, both positive and negative, and the externality's effect on marginal private benefit and marginal social benefit.
![National Bureau of Economic Research: Measuring Positive Externalities [Pdf] Activity](https://d15y2dacu3jp90.cloudfront.net/images/attachment_defaults/resource/large/FPO-knovation.png "National Bureau of Economic Research: Measuring Positive Externalities [Pdf] Activity")
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National Bureau of Economic Research: Measuring Positive Externalities [Pdf]
This research paper describes how the installation of an anti-theft device on cars has helped reduce crime in general in some areas. The concept of positive externalities can be seen in this example.
Tutor2u
Tutor2u: Market Failure Positive Externalities
This site examines how society can benefit by producing and consuming more of a product that causes a positive externality.
Khan Academy
Khan Academy: Socially Efficient and Inefficient Market Outcomes
Practice what you've learned about marginal social cost and marginal social benefit in this four-question exercise.