I live in Southern California, and our temps can range from just below freezing to over 100° (in the same month ! seriously). I keep mine in the pantry, along with my flour, baking soda and cornstarch. Never noticed an issue, but I do look at the expiration date, and make sure its still good before I dump it into a recipe. Luckily we're not too humid here, so that's not an issue. The moisture is what I'd be afraid of in the fridge.

Check the input on a more recent question about storing chocolate -- I like the answers. To me "cool dry place" means not in the fridge (or it would say "refrigerate after opening." Answers above show that all options work, oddly enough. And if you can find a store like the one I used to own, you can buy it in bulk, any quantity. And personal experience for me, the 5# can I bought for personal use did not show any deterioration.

I use organic, and there is an expiration date on it so what i do is leave it in the freezer. Been doing it for years, and have no issues.

I leave mine in the pantry and never have a problem with it. But I go through it fast and replace it often.

I say leave it in the fridge if you don't use it very often, using and placing it back in the fridge as quickly as possible to minimize condensation. Maybe put it in a freezer bag too?

You're going to want to replace your baking powder at least once a year anyway. If you're not going through a whole can a year they sell half cans, I don't remember them being much cheaper, but it's less of a waste of product and space.

drbabs, I always like a little disagreement! makes things more interesting, and I learn more.

Sorry to disagree with you folks, but I keep mine in the refrigerator. No clumping and it works just fine.

Fridges are quite humid, so I think it would clump up in there, even with the lid on. As hardlikearmour says, taking it out and putting it back would probably allow moisture in. Definitely keep it in the cupboard.

I'd keep it in the cupboard. I'd worry about condensation forming in the can if you pull it out of the fridge, use it, then put it back in the fridge.