The nature of thermodynamics and the basis of thermostatistics. Postulates of thermodynamics. Conditions of equilibrium. The Euler equation and Gibbs-Duhem relation. Reversible processes and the maximum work theorem. Legendre transformations. The extremum principles for the thermodynamic potentials. Maxwell relations. Stability of thermodynamic systems. First order phase transitions. Critical phenomena. The Nernst postulate. Irreversible thermodynamics postulate. Irreversible thermodynamics.