You can find the history of chiropractic on various chiropractic web sites, so I won't go into it here. This is both good and bad. It can be frustrating when shopping for a chiropractor, but it's also a sign of growth and development. Others work with the musculature under the notion that balanced muscles will result in properly aligned vertebrae.
Most practitioners use a hybrid of several techniques.
This has led to accusations of chiropractic as a placebo therapy, whereby the actual application means nothing, and the mental perception of the patient is the only healing force. I will concede that in some cases, the placebo principal is truly at work. This is particularly in the cases I've seen where doctors seem to be getting their patients well by way of their unusually positive attitude, in spite of their sloppy or poor adjusting skills. However, for an effect to be a true placebo effect, it must be only temporary. Chiropractic is essentially a preventive form of health care.