Our 7lb ShihTzu loves to come with us, but often can't walk as far as we do.  Now we back pack him one way and he walks the return trip. The medium is the perfect size for him.  Also had the small Snoozer but it was too cramped for him.  He loves this one though - it's easier to get him in and out of.  We hope to use it for airline travel, but so far we have done just long walks.  Excellent place for him to be while we eat at outdoor restaurants and cafe's. He is very happy sitting in his Snoozer!!