Far from hurting the little yeast cells, freezing puts them in a state of suspension. Keep them in an airtight container where they are protected from oxygen and humidity. The glass jar the yeast comes in is usually just fine. For bulk yeast, I use a canning jar.
You can use the yeast straight from the freezer. Sprinkling it into room temperature liquid wakes them right back up again. I've kept dry yeast in the freezer for months past its expiration date with no discernable change in how well the yeast works in my baked goods. I'm currently still working through a bulk bag I picked up over two years ago!
If you're ever nervous that the yeast may no longer be good, just test it out in a little warm water with a pinch of sugar. If it starts bubbling after a few minutes, then it's good to go. Also, don't try freezing fresh "cake" yeast; it's different and doesn't usually react as well to being frozen.
Where do you store your yeast?
Related: Working with Yeast: Be Not Afraid!
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