Homeopathy began some two hundred years ago when a German doctor, Samuel Hahnemann, began to question the medical practices of his time. What developed was a very safe system of medicine, with no undesirable side effects or risk of addiction, which is suitable for everyone - babies and children, teenagers and the elderly - and may even be used in pregnancy.
Hahnemann rediscovered a phenomenon, originally observed by Hippocrates in Ancient Greece. He found that if Peruvian Bark, from which quinine is derived and used to treat malaria, was given repeatedly to a healthy person, it would produce the symptoms of malaria in that person. He surmised this was why quinine was able to cure malaria in a sick person. He continued to experiment with other substances, observed the same results and like cures like became the first law of homeopathy.
There are thousands of homeopathic medicines, or remedies, each of which has been tested or proven in that way. The remedies come from different sources, for example Phosphorous and Sulphur are derived from minerals; Arnica and Chamomilla from plants; and Sepia and Apis from animal sources (the Cuttlefish and Honey Bee respectively). Each remedy has a picture built up from the both the physical and emotional symptoms arising in the proving and it is the homeopath's job to match the patient's overall discomfort to the picture of a remedy. This is why a homeopathic consultation is so much more detailed than most people are used to; the homeopath needs to know as much as possible about you and the way you express an illness, in order find your closest match. Four people, all complaining of a sore throat, may each need a different remedy depending on what the sore throat is like for them.
Hahnemann was also unhappy with the large doses of medicines employed at the time and began experimenting with increasingly smaller doses. He found the more dilute a substance, the more effective it was in treatment. And so we have a second law - use the minimum dose. Some very sophisticated dilutions, known as potencies, are employed today and are one of the reasons why homeopathy is so safe to use.