Other
East Tennessee State University: Explicit and Implicit Costs
This resource provides a good example of the differences between explicit costs and implicit costs using the ownership of a pizza restaurant as an example.
Sophia Learning
Sophia: Making Decisions
Notes and a video clip provide students with an introduction to the idea of marginal analysis and of how consumers and producers make decisions.
Wikimedia
Wikipedia: Opportunity Cost
Provides a clear explanation of opportunity cost in a way that is accessible to those new to economics. Includes links to terms that may require further clarification.