Content license compatibility

In fact, the only compatible "licenses" in popular usage are ones which enable one-way compatibility:

• Public domain - not a true license, allows reuse under any terms, without restrictions.
• CC-BY - allows reuse anywhere, under any license or copyright, provided attribution is given.

One key difficulty now with sharing content is the popularity of various licenses, especially Creative Commons, which are not all compatible. For example, NonCommercial and NoDerivatives clauses break compatibility with true open licenses such as CC-BY-SA (using only the the Attribution and ShareAlike clauses) as used by Appropedia and Wikipedia.

This is unhelpful in creating a successful commons, but is often an unintended consequence as the implications of these license choices are poorly understood among content creators.

• An Introduction to Creative Commons for an overview.