This is the very last pose in Ashtanga Yoga's Primary Series, and aside from working your booty and thighs, this backbend also offers an awesome stretch for your abs, chest, and neck.
This pose takes special attention in order to prevent straining your neck, so move into Bridge pose slowly. Lie on your back and plant your feet one third of the way toward your tush, with your heels touching and your toes wide. Open your knees out to the sides slightly. Cross your arms and place your hands on opposite shoulders. Arch your back by lifting your chest, and bring the top of your head to the floor. Now press into your feet to lift your hips off the ground, straightening your legs and coming into the full expression of the pose. If this feels like too much, keep your hips on the floor and rest your arms on the mat parallel with your torso. After five breaths, bend your knees and lower your hips to the floor.
If this pose doesn't seem like a good idea, opt for Fish pose as a less intense variation.