In macroscopic approach, certain quantity of matter is considered without taking into account the events occuring at molecular level. In other words, this approach to thermodynamics is concerned with gross or overall behaviour. This is known as classical thermodynamics.

The microscopic approach considers that system is made up of a very large number of discrete particles known as molecules. These molecules have different velocities and energies. The values of these energies are constantly changing with time. This approach to thermodynamics which is concerned directly with the structure of the matter is known as statistical thermodynamics.