Permission to use copyrighted material must be obtained when fair use, face-to face teaching or one of the other exemptions do not apply. The only other legal option is to not use the material. When permission is needed make sure you are getting permission from the person who has the authority to give it. Permission must be obtained from the actual copyright holder. This is not necessarily the author; it is generally the publisher. Call or e-mail the person, publisher and or Webmaster to confirm copyright ownership. In instances where there are multiple copyright owners it may be necessary to obtain permission from all of them. Be sure you investigate this possibility.
It is also important to communicate with the copyright owner(s) the exact type of right you need. You don't want to pay for more than is necessary but at the same time you don't want to have to go back and get additional permissions. Clearly state your need and the use you will be making of all the parts of the work you will be using. Don't be afraid to negotiate the fees.
Even though permission is frequently given, there is no once for all permission and so for course packs, syllabi, reserves and the like permissions may need to be obtained for every semester the work is used. Although royalties vary dramatically they are usually affordable. Never-the-less this is an important consideration as they may be assessed every time permission is granted. Another consideration is that these fees may be passed on to the students receiving the documents.
When requesting permission, be sure to get it in writing and keep it on file. If you are uploading the material to a Web site and you have made a good faith effort to get permission but are unable to locate the owner, make a disclaimer to the effect that you will remove the material at the copyright owner's request (see DMCA) Digital Millennium Copyright Act (DMCA)
For more information about getting permission peruse the Stanford University Libraries Copyright & Fair Use Web site: Permission: What is it? Why do I need it?.
For detailed information on getting permission for print, images/photos, music, audiovisuals and movies see Public Performance Licensing Getting Permission: Where and How at Washington State University.