How do I make and keep cookies crisp?

Another key point is to make sure that you store crisp cookies with crisp cookies ONLY and keep soft cookies stored separately. A soft cookie's moisture can soften an entire batch of crisp cookies if they are stored together. This also means that if you underbake some cookies in the same batch (like Thirdchild mentioned), they can still be slightly soft and soften the cookies that were baked for longer.

Amanda's Chocoate Oatmeal cookies are wonderfully crisp. Perhaps it is the use of shortening in the recipe? I always keep my cookies in a tin with a tight fitting cover. They stay beautifully crisp. Also, make sure you are baking the cookies long enough. An underbaked cookie will become soft cookie more easily!

I think that it might be hard to keep an oatmeal cookie crisp because the oats soften as well, but have you tried toasting them first?

Thanks for the tips. I'm going to try them all, and I guess I better invest in a glass container! I wonder why glass???

My husband prefers crisp cookies. These are some of the tips I've picked up over the years:
Use a higher proportion of white sugar to brown sugar. (Brown sugar contains molasses which draws water in and keeps baked goods soft.) Use a little extra baking soda. Use butter and leave room for cookies to spread. Pat down the balls of dough so they're thin and flat when you put them on the cookie sheet. Err on the side of slight overbaking. (not burning. you didn't need me to say that though, right?)

To keep them crisp, let them cool completely and store them in an airtight container. ( i never heard of the glass container trick, but it's worth a try.) If they soften anyway, you can run them in a 300 degree oven for about 5 minutes. When they cool, they'll be crisp again.

Cookies kept in plastic containers get soft quickly while cookies kept in glass containers stay crisp much longer.