I was at a friend's house today and she asked me "Do you know when car seats expire?" What?!! I did a double take. Am I the only one that has never heard of this before? So I turned to the internet to do research, and sure enough, car seats expire. Apparently consignment stores and sales will not even take them within a year or two before the expiration date. I always just thought that you buy a carseat with your first kid and use if for the next 15 years for any other kids you have. We actually used a hand-me-down we got for free for 2 1/2 years for Kirsten. Most car seats have an expiration date printed on them, or if they don't, it is 6 years from the manufacture date. Something about the plastic breaking down and weakening over time. If you want more information, here is a link to about.com that explains why they expire.