answered Nov 28, 2010 at 10:01AM
Homeopathy is the practice of diluting a substance in water until there is less than a molecule of that substance present in the water. The theory is that the water retains some memory of that substance, and the substance has some intrinsic effect against a disease.
In addition to not having any scientific rationale, studies have shown it to be no more effective than placebo. They also tend to be expensive, while offering no additional benefit over the water from the tap.