  The second law of thermodynamics is probabilistic in nature. Its formulation
requires that the state of a system be described by a probability distribution.
A natural question, thereby, arises as to whether a prior knowledge about the
state of the system affects the second law. This question has now been nurtured
over a century and its inception was done by C. Maxwell through his famous
thought experiment wherein comes the idea of Maxwell's demon. The next
important step in this direction was provided by L. Szilard who demonstrated a
theoretical model for an information engine incorporating Maxwell's demon. The
final step that lead to the inter-linkage between information theory and
thermodynamics was through Landauer's principle of information erasure that
established the fact that information is physical. Here we will present an
overview of these three major works that laid the foundations of information
thermodynamics.
