In the present scenario, internet is among the basic necessities of life. Internet has changed each and everybody's lives. So confidentiality of messages is very important over the Internet. Steganography is the science of sending secret messages between the sender and intended receiver. It is such a technique that makes the exchange of covert messages possible. Each time a carrier is to be used for achieving steganography. The carrier plays a major role in establishing covert communication channel. This survey paper introduces steganography and its carriers.