Summary: This hood should have been supplied with the lens as purchased new. It works great and all, but Canon should have supplied it with their lens. They supply lens hoods for their other expensive lenses.
Summary: This is genuine canon, made in Japan. Although it's appears to be only a piece of plastic, it is very essential if you are serious about photography under bright sunlight. Look at strengths above, there is no reason not to have one. I have a Hoya multi coated filter on my lens and this hood still fits perfectly. I love the dual protection. You already spend about a grand on your lens, don't be cheap on the lens hood.
Pros: Excellent Quality Made In Japan Great protection for the front element Improved contrast in bright sunlight
Summary: Essential but not included with the Canon EF-S 17-55mm f/2.8 IS USM lens. As expected, it is well matched with the lens and does an effective jog of controlling light entering the lens without intruding on the image at any zoom setting. It is even possible to (carefully) adjust a circular polarizer with the hood in place.
Pros: Durable, Easy To Use, Improves Product Function