First of all, do you know for sure that it is crystal? Crystal stemware is often, but not always, heavier than glass. When gently tapped with your fingernail, crystal emits a melodious ringing sound. Glass does not.
Crystal contains lead, added for strength and creating the sparkle associated with it. Old pieces that feature elaborate detail can be quite valuable.
Look closely at the bottom of the glass as some marks are difficult to see. Use a magnifying glass. Many manufacturers marked their stemware with labels. Labels can fall off over the years.
Research your stemware on Replacements which features a huge inventory. You can sign up to help you identify your pieces. Glass Lovers Glass Database may be helpful as well. You can also check your local library which should have several books on antique and vintage crystal.