The microchip, which is about the size of a grain of rice, is injected by a veterinarian or veterinary technician just beneath your pet's skin in the area between the shoulder blades. This is usually done without anesthesia, and the experience can be compared to getting a vaccination.
While it may be comforting to know the microchip won't get lost or damaged, and that it will probably last the pet's lifetime, the microchip is useless if you're not updating your contact information with the registry. If your pet has been microchipped, keep the documentation paperwork so you can find the contact information for the registry. If you don't have the documentation paperwork, contact the veterinarian or shelter where the chip was implanted.