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All content by Kyle E. Mitchell, who is not your attorney.

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Open Source Software License Reading Listrecommended program of reading, comparison, and analysis

A number of people have asked me for hints on which open source licenses to read, in order to develop a working understanding of the field. The following list suggests a number of licenses, in a specific order, designed to help develop understanding.

Send suggestions, corrections, and feedback via GitHub.

Notes to Readers

When this program says read, read very carefully, at least twice. Take notes as you go. Don’t skip any terms. Get as much out of each license as possible.

When this program says compare, run a machine text-to-text comparison, using a word processor’s compare-documents feature. Then read the comparison very carefully, at least twice. Ask yourself: Why do these licenses differ? Get as much out of each comparison as possible.

When this program does not explicitly tell you to compare, compare anyway. Don’t take any license on its own. Ask how it differs from other forms, in style and in substance. Ask yourself why it differs.

This list might seem long, but each license is fairly short, as legal reading goes. In the end, there is not that much source material.

Be a legal vampire. Suck every last drop of meaning from every last license section and comparison. That effort, not finishing this list, will determine what you get out of this program.

Group 1: Permissive Licenses

Series 1: Academic Licenses

  1. Read The MIT License, a very popular open source license.

    Read The MIT License, Line by Line.

  2. Read The ISC License, a fairly popular open source license.

    Compare to The MIT License.

  3. Read The Two-Clause BSD License, a very popular open source license.

  4. Read The Three-Clause BSD License, a fairly popular open source license.

    Compare to The Two-Clause BSD License.

  5. Read The Four-Clause BSD License, a historically significant, now discouraged, open source license.

    Compare to The Three-Clause BSD License.

  6. Read The BSD-2-Clause Plus Patent License, an relatively new open source license.

    Compare to The Two-Clause BSD License.

Series 2: Agreement-Style Licenses

  1. Read The Artistic License 2.0, a popular open source license among Perl developers.

  2. Read The Apache License, Version 2.0, a very popular open source license.

  3. Read The Educational Community License, Version 2.0, a niche open source license.

    Compare to The Apache License, Version 2.0.

  4. Read The Academic Free License v. 3.0, a niche open source license.

Group 2: Copyleft Licenses

Series 1: OSLs and GPLs

  1. Read The Open Software License v. 3.0, a niche open source license.

    Compare to The Academic Free License v. 3.0.

  2. Read The Non-Profit Open Software License v. 3.0, an even more niche open source license.

    Compare to The Open Software License v. 3.0.

  3. Read The GNU General Public License, version 3, a popular open source license.

  4. Read The GNU Affero General Public License, version 3, a popular open source license.

    Compare to The GNU General Public License, version 3.

  5. Read The GNU General Public License, version 2, a very popular open source license.

Series 2: Copyleft Background

  1. Read Copyleft: Pragmatic Idealism.

  2. Read Why you should use a BSD style license for your open source project.

  3. Read Unhappy Coincidences.

Series 3: Weak Copyleft

  1. Read The GNU Lesser General Public License, version 2.1, a niche open source license.

    Compare to The GNU General Public License, version 2.

  2. Read The Mozilla Public License, version 2.0, a niche open source license.

  3. Read The IBM Public License v1.0, a historically significant, now superseded, open source license.

  4. Read The Common Public License 1.0, a historically significant, now superseded, open source license.

    Compare to The IBM Public License v1.0.

  5. Read The Eclipse Public License 1.0, a historically significant, now superseded, open source license.

    Compare to The Common Public License 1.0.

Series 3: License Compatibility

  1. Read The Eclipse Public License 2.0, a niche open source license.

    Compare to The Eclipse Public License 1.0.

  2. Read The Common Development and Distribution License 1.0, a historically significant, now discouraged, open source license.

    Compare to The Mozilla Public License, version 2.0.

Series 4: Reciprocal Licenses

  1. Read The Sleepycat License, a historically significant, now discouraged, open source license.

    Compare to The Two-Clause BSD License.

  2. Read The Q Public License Version 1.0, a historically significant, controversial open source license.

  3. Read The Reciprocal Public License 1.5, a historically significant, controversial open source license.

Group 3: Antilicenses

  1. Read WTFPL, a popular open source license.

  2. Read The Unlicense, a popular open source license.

  3. Read The Zero-Clause BSD License, a niche open source license.

    Compare to The Two-Clause BSD License.

  4. Read The Fair License, niche open source license.

Review

  1. Read The MIT License.

  2. Read The Three-Clause BSD License.

  3. Reread The Apache License, Version 2.0.

  4. Reread The GNU General Public License, version 2.

  5. Reread The GNU General Public License, version 3.

  6. Reread The GNU Affero General Public License, version 3.

  7. Reread The Mozilla Public License, version 2.0.

Bonus Group

Series 1: Third-Wave Copyleft Licenses

Note: As of early 2019, whether these licenses count as open source software licenses remains controversial.

  1. Read copyleft-next.

  2. Read Parity.

  3. Read The Server Side Public License, Version 2.

    Compare to The GNU Affero General Public License, version 3.

  4. Read The Cryptographic Autonomy License.

Series 2: Ethical Licenses

Note: As of early 2019, these are not broadly considered open source software licenses.

  1. Read The Hacktivismo Enhanced-Source Software License Agreement.

  2. Read The Peer Production License.

Further Reading

Free Online

In Print

Teaching Notes

This program makes crucial use of Lawrence Rosen’s AFL and OSL. Those are not particularly popular licenses. But the textual comparison directly emphasizes the basic difference between permissive/academic and copyleft/reciprocal. I don’t think there’s a better license pair—BSD and Sleepycat?—to drive that difference home.

The licenses under Review will be the most relevant and popular for most practitioners. If I really, really had to cut this course down, I’d assign just those licenses. If I had to cut the course down substantially, but not that far, I would likely skip the reciprocal licenses and antilicenses, or cull them down to RPL 1.5 and WTFPL or Unlicense, respectively.

Your thoughts and feedback are always welcome by e-mail.

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