This document summarizes quantum cryptography and the BB84 protocol. It discusses how quantum cryptography is provably secure and can detect tampering through measurement-induced perturbations. The BB84 protocol is then explained, where Alice encodes random bits in one of two bases and sends quantum states to Bob, who measures in a random basis. They compare bases to determine a secure key, and any errors indicate potential tampering by Eve. Current implementations can transmit keys over 200km of fiber or 10km free-space. Future applications may include satellite-based quantum cryptography links.