London Broil comes from the top round (upper back leg). It is a lean roasting cut, similar to others from the same region - Eye of Round, and Tri-Tip. As with all lean cuts, cooking only to the desired level of doneness (rare or medium rare is recommended) and not beyond is imperative. Overcooking a lean cut will make for dry meat. We use digital instant read thermometers in our home kitchens to ensure the right internal temp and no higher is reached.
These cuts can be grilled, pan fried, or roasted in the oven. Just don't over cook it.
Photo Credit - Normandy Alden