Pizzaholic,
Dry yeast, either active dry yeast (ADY) or instant dry yeast (IDY), has a good shelf life--about 1 year if the package is unopened (and not refrigerated), and 6 months if tightly resealed and refrigerated after opening and, for added protection, stored in an airtight container. If frozen (also in an airtight container) the yeast will last almost indefinitely (although yeast producers usually recommend a much shorter time period—about a year). In my case, I take the one-pound bag of yeast, tightly close the opening by folding the top under, wrap a rubber band around the bag to keep it tightly shut, and put the bag into an airtight container. I have yeast that is several years old using that approach.
Peter