Near-Earth asteroid 2005 YU55 will pass within 0.85 lunar distances (325,000 kilometers or 201,700 miles) of the Earth on November 8, 2011. The close approach by this relatively large 400 meter-sized asteroid will present an excellent opportunity for ground-based optical, near infrared, and radar observations. The object will reach a visual brightness of 11th magnitude and should be easily visible to observers in the northern and southern hemispheres. Since the asteroid will approach the Earth from the sunward direction, it will be a daylight object until the time of closest approach. Although classified as a potentially hazardous object, 2005 YU55 poses no threat of an Earth collision over at least the next 100 years. This will be the closest approach to date by an object this large that we know about in advance. An event of this type will not happen again until 2028 when asteroid 2001 WN5 will pass to within 0.6 lunar distances.