There are four laws of thermodynamics.
Zeroeth Law of Thermodynamics: Two systems in thermal equilibrium with a third system are in thermal equilibrium to each other.
First Law of Thermodynamics: The change in a system's internal energy is equal to the difference between heat added to the system from its surroundings and work done by the system on its surroundings.
Second Law of Thermodynamics: It is impossible for a process to have as its sole result the transfer of heat from a cooler body to a hotter one.
Third Law of Thermodynamics: The entropy of a perfect crystal at absolute zero is exactly equal to zero.