Bates Crates attach to a porter rack on the front of your bike. They're designed to be held on with bungee cords which will keep the crate and your goods strapped down tight!
There are eye-straps at the front of the crate to attach the bungees to. Why bungee cords you ask? This way you can take it off with ease, so it dosen't get stolen, or take it right in the store with you and use it as your basket! If you need to use your porter rack to carry something big, its still available.
What kind of racks does it work with? if you're ordering one for your Trek Echo, you already have the rack and don't have to worry!
Otherwise you are going to need a porter rack. There are few companies making them- I like Cetma the best. They make a good rack at a reasonable price. Granted, they're not the most beautiful racks out there, but they're very reliable and they're also made by hand in Eugene, Oregon by one guy...just like Bates Crates!