Here are the most common and popular styles of bike locks. U-Lock: Most widely used, it has a horseshoe shape, which can neatly accommodate locking up most bicycles. The primary advantage of this bike lock design is that it limits leveraging, which is what a bike thief does with a crowbar (or equivalent item) to pry open a lock. A U-Lock is, by its design, a great bike theft deterrent so long as it's not oversized relative to the bike it's protecting. The ideal fit is just big enough to lock up your bike, yet with a mind to smaller is better, since that means less opportunity for a bike thief to pop apart the lock. A U-Lock has a somewhat bulky lock mechanism, which is good since it will resist chisels, screwdrivers, hammers, etc. They are sometimes called D-Locks as well. Since the U-Lock has such a strong bike theft prevention design, many manufacturers, such as Kryptonite, offer a warranty program against bike theft. Chain: a bike chain uses specially designed links which resist being sawed into or pried open by hacksaws or chisels. The adage "a chain is only as strong as its weakest link" certainly comes into play here! You must pair your chain lock with an equally, if not more, strong padlock to prevent your bike from being stolen. Cable: These are versatile in many bike locking situations, though not as strong protection as other bike lock options. Sometimes it's good to use a bike cable lock in combination with an additional, sturdier bike lock. Bike Club: just like the automobile analog, this lock type is placed across the wheel and bike frame and locked into place. It's difficult to cut a bike club style lock, or to leverage it off, but you must be diligent to properly use it to get the maximum security. Cuff Locks: Picture a set of handcuffs. Yep, same idea. The likely weakest link here is the middle hinge, so the bike lock manufacturer must be certain to build this part especially strong to resist tampering or breaking. How to Lock Up Your Bike: Remove the front wheel if possible. As well, remove the seatpost and bike saddle if it's easy to be taken off. If you leave your saddle on your bike, take off the saddle bag. Remove other unsecured bike gear, like bike frame pumps or bike lights. Your goal in locking up your bike is to present a picture of above-average resistance which will otherwise convince a thief that it will take too much effort to try to steal your bike. If you can use 2 locks, more power to you, bike thieves will oftentimes just move pass by your bike figuring it's too much trouble. It's always a good idea to register your bike at your local law-enforcement branch, or to secure a bike license for it. Note your bike frame serial number, if you can find it, usually under the bottom bracket. Choose a bike lock that offers theft-protection in the form of a warranty or monetary guarantee. Just remember to mail in all the required paperwork to register your bike lock. Don't lock your bike to chain-link fence, since all it takes is wire cutters to get to your bike. Try to identify underground parking lots that allow bike parking, ideally with video surveillance. It's true, there will be less foot traffic to deter bike thieves, but then again, your bike may never be seen to begin with. Don't lock your bicycle in the same spot every day, since thieves might catch on to your daily pattern. Lock your bike next to other bikes whenever you can. You should keep an extra key at home, or the bike combo number if that's the case. You should periodically squirt a Teflon imbued lubricant in your bike locking mechanism to keep it working right. Your bike is important to you, for fun riding, for work, for many other things, so QBike offers a wide selection of bicycle locks from the top manufacturers.