This category is for articles about licenses which:

  1. Contrary to the usual application of copyright law, aim to enable each recipient to help himself and to cooperate with others, and
  2. Require that modified versions be distributed wholly under the same licence ("share and share alike")

Note: this category differs substantially from Category:Free and open-source software licenses in that it is not limited to software, and not all free software licenses are copyleft (some are permissive, like those of BSD and MIT).