+Externalities are the unseen echoes of economic actions, costs or benefits imposed on a third party not directly involved in a transaction. They represent the spillover effects, like the burden of [Pollution](/wiki/Pollution) from a factory or the unexpected beauty from a neighbor's [Garden](/wiki/Garden). These unpriced impacts influence societal welfare, often necessitating public policy.
+## See also
+- [Market Failure](/wiki/Market_Failure)
+- [Public Goods](/wiki/Public_Goods)
+- [Social Cost](/wiki/Social_Cost)
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