In a quantum mechanical system, far more exotic spin orderings than simple magnetism are possible, in which entanglement and superposition play a crucial role. A spin liquid is one such exotic ordering; a system of spins which are far more entangled than expected in magnets, which lacks magnetic ordering at any temperature. In this talk, I will discuss spin liquid systems, focusing on what spin liquids are, why we are interested in finding them, where we expect them to be present and the difficulties in positively identifying spin liquids in nature.