  The aim of this book chapter is to indicate how quantum phenomena are
affecting the operation of microscopic thermal machines, such as engines and
refrigerators. As converting heat to work is one of the fundamental concerns in
thermodynamics, the platform of quantum-thermal machines sheds light on
thermodynamics in the quantum regime. This chapter focuses on the basic
features of quantum mechanics, such as energy quantization, the uncertainty
principle, quantum coherence and correlations, and their manifestation in
microscopic thermal devices. In addition to indicating the peculiar behaviors
of thermal-machines due to their non-classical features, we present
quantum-thermodynamic signatures of these machines. Any violation of the
classical bounds on thermodynamic measurements of these machines is a
sufficient condition to conclude that quantum effects are present in the
operation of that thermal machine. Experimental setups demonstrating some of
the results are also presented.
