Lie flat on your back. Extend your arms so they're against the sides of your body with your palms pressing into the floor, or bend your elbows and place your palms under the back of your head.
Lift both legs straight up toward the ceiling, continuing to engage your abs.
Keeping your core strong, slowly lower your right leg down toward the ground until it is hovering a few inches off the floor.
Then slowly switch your legs, lifting your right leg back up as you lower your left leg down toward the ground.