Many publishers’ policies on posting articles are available at the SHERPA/RoMEO site.
If the publisher is not listed on the site, then it will be necessary to contact them directly. Suggested templates for permission requests are available at the SHERPA site.
Author(s) of work(s) own the copyright unless transferred to another.
Many publishers ask that author(s) transfer their rights, but authors do have options other than giving up their copyright ownership entirely.
Author’s can negotiate with publishers to retain certain rights.
For more information on author’s rights consult SPARC (Scholarly Publishing and Academic Resources Coalition).