Most non-copyleft OSS licenses are compatible in some form, including with copyleft licenses such as the GPL; when used in a combined work, the combined work's

Most non-copyleft OSS licenses are compatible in some form, including with copyleft licenses such as the GPL; when used in a combined work, the combined work's license essentially reverts to the most restrictive of the licenses. In some cases, such as with WinObjC, reverting to the most restrictive license makes the work unsuited for its intended purpose. However, many copyleft OSS licenses have clauses that are genuinely incompatible with both other copyleft licenses, and less-liberal OSS licenses -- in such cases it's impossible to legally combine code under the licenses. In your example, the CDDL and the GPL have incompatible copyleft restrictions; your resulting program wouldn't be distributable under the provided licenses. A more common incompatibility example is that of the OpenSSL license and the GPL; GNU maintains a fairly complete list of incompatibile licenses here: http://www.gnu.org/licenses/license-list.en.html#GPLIncompatibleLicenses http://www.gnu.org/licenses/license-list.en.html#GPLIncompat...