The Eclipse Public License (EPL) is an open source software license used by the Eclipse Foundation for its software. It replaces the Common Public License (CPL) and removes certain terms relating to patent litigation.
The Eclipse Public License is designed to be a business friendly free software license, and features weaker copyleft provisions than contemporary licenses such as the GNU General Public License (GPL). The receiver of EPL-licensed programs can use, modify, copy and distribute the work and modified versions, in some cases being obligated to release their own changes.
The EPL 1.0 is not compatible with the GPL, and a work created by combining a work licensed under the GPL with a work licensed under the EPL cannot be lawfully distributed. The GPL requires that "[any distributed work] that ... contains or is derived from the [GPL-licensed] Program ... be licensed as a whole ... under the terms of [the GPL].", and that the distributor not "impose any further restrictions on the recipients' exercise of the rights granted". The EPL, however, requires that anyone distributing the work grant every recipient a license to any patents that they might hold that cover the modifications they have made. Because this is a "further restriction" on the recipients, distribution of such a combined work does not satisfy the GPL.
The EPL, in addition, contains a patent retaliation clause, which is incompatible with the GPL for the same reasons. But GPL version 3 also has a patent retaliation clause in section 10.
Derivative works Edit
The EPL allows the developers of changes and additions of EPL-licensed code to make their own license under any type of license they choose for the changes and additions separately. However, the EPL-licensed part of their derivative software product should be licensed under EPL license, but the developers can have private right about the portions of changes and additions. 
In EPL, as with every free software licence, the contributor can charge money for programs which the contributor changed and added to the program. Also, there are no restrictions on providing source code. The contributor can make, use, sell, offer to sell, import and transfer the contribution. 
The EPL-licensed portions of the derivative software product must be licensed under an EPL-license, but the improvements and additions could be written separately as their own license.
Later versions Edit
If a new version of the EPL is published the user/contributor can choose to distribute the software under the version he received it with or upgrade to the new version.
The significant difference between the GPL and EPL is that EPL allows the developers to make their own license for the portions of their improvements or additions separately from the EPL-licensed code, if the EPL-licensed portions of their derivative software product are licensed under the EPL license agreements. In other words, the developers can keep the improvements or additions as proprietary. In addition, EPL was based on the CPL,  but there are some differences between the two licenses:
- The Eclipse Foundation replaces IBM as the Agreement Steward in the EPL
- The EPL patent clause is revised by deleting the sentence from section 7 of the CPL
- The Eclipse Public License, version 1.0
- Eclipse Public License FAQ
- EPL on OSIfr:Eclipse Public License
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