In a bodyscan you lie down or sit, close your eyes and move your attention through your body, from the soles of your feet up to the crown of your head. You don't use your hands for this, only your attention. It sounds very simple, and many people are surprised by how much they suddenly notice.
The bodyscan became widely known through Jon Kabat-Zinn and his MBSR program (Mindfulness-Based Stress Reduction). The idea of moving attention systematically through the body is much older, though. You find it in the Vipassanā tradition, in yoga and in various forms of qigong, for example in the Chanmi Qigong practice of the Inner Smile.

What happens in a bodyscan? 身体
You go through the body area by area, the feet, the legs, the torso, the arms and the head, and simply notice what is there. A full session usually takes somewhere between twenty and forty-five minutes. In one place you may feel a pulsing, in another warmth, and some areas feel numb or empty at first. In other words, you start to experience your body from the inside, as a living landscape and not only as something you look at in the mirror.
In the mindfulness tradition the point isn't to change anything. Tension is allowed to be tension. Interestingly, this non-judging attention alone often changes your relationship with the body, and tension sometimes lets go on its own once it gets some space.
The Inner Smile 微笑
In Chanmi Qigong there's a practice that gives the bodyscan a different quality, the Inner Smile. Instead of just observing the body neutrally, you meet it with friendliness and joy, organ by organ and joint by joint.
Many people have a rather critical relationship with their body. It's too heavy, too tired, it hurts somewhere. The Inner Smile turns this around a bit. It isn't an affirmation along the lines of "I'm beautiful just the way I am." It's more like greeting an old friend you haven't seen in a long time.

Bodyscan and Reiki 靈氣
Anyone who gives Reiki knows that the body responds under the hands with warmth, pulsing, tingling or coolness. In Shingon Reiki, breath, mantra and inner images are added to the hands. The bodyscan is a good foundation for this kind of perception, because if you've never felt your own body from the inside, you'll probably notice less in a Reiki treatment as well. Put simply, the two practices complement each other. A regular bodyscan refines your perception, and Reiki gives that perception something to work with.
A relaxation meditation is mainly about letting go and coming to rest, which is valuable. In the bodyscan and in Shingon Reiki, relaxation is more of a starting point, the ground on which finer perception can grow.
Common obstacles 道
The classic one is falling asleep. You lie comfortably, relax, and wake up twenty minutes later. That mostly shows how tired you actually are, and it often helps to practice sitting or at a time of day when you're more awake. Then there are wandering thoughts. Your attention is supposed to be in your left foot, and you're planning dinner. Noticing this and coming back is the actual practice. Unpleasant sensations or areas where you feel nothing at all are also part of it. They're information too, and if something gets really uncomfortable, you can simply move on. And if forty-five minutes don't fit into your day, ten minutes in the morning or evening are a good start. Doing it regularly matters more than doing it perfectly.
I describe more of these obstacles in the article on the nine resistances in meditation.

The bodyscan needs no prior knowledge, no initiation and no equipment, which makes it one of the easiest ways to refine your body awareness. Which part of your body do you notice first when you close your eyes?
Your path into depth
The bodyscan is a good beginning. In Shingon Reiki, energy work, mantra and initiation build on it. If you like, have a look at which entry fits you.
Your Path in Shingon Reiki Relaxation Meditation