Generally there are two types of Reiki: the traditional Japanese and the American one. From these many different techniques come from, and they differ just slitly.

I think there are different reasons to explain these diversity: first of all Reiki is a oriental phylosophy whichhas many points in common with other olistic disciplines (the Universal Energy understood like totality, the existance of energetic channels inside the metaphysical body, the existance of simbols and mantra able to call the energy etc..).

The explanation of Reiki is in function what we know about other disciplines. Because Reiki is a pure flowing of Energy, it is often used with other techniques, with the purpose of rise the efficiency of the treatment.

Because it is a phylosophy of life, Reiki could be

explained according to the enviroment in which it is. It is not a chance that in the Japanese tradition Reiki is more spiritual (the healing comes from the bilance with Vital Energy) while in the western one is more material (concentrate on physical benefit).

We can't avoid to remember the will of the different teachers who "personalise" their own discipline, adding simbols, rules, meanings which are part of the culture and the learning of the teacher. In that case we aren't facing Reiki discipline anymore, but many techniques that leave this discipline as the least important part. This doesn't mean that those techniques “don't work” or that they give less result, simply they are not the pure Reiki discipline that Maestro Usui was using.