  The seminal work by Sadi Carnot in the early nineteenth century provided the
blueprint of a reversible heat engine and the celebrated second law of
thermodynamics eventually followed. Almost two centuries later, the quest to
formulate a quantum theory of the thermodynamic laws has thus unsurprisingly
motivated physicists to visualise what are known as `quantum thermal machines'
(QTMs). In this article, we review the prominent developments achieved in the
theoretical construction as well as understanding of QTMs, beginning from the
formulation of their earliest prototypes to recent models. We also present a
detailed introduction and highlight recent progress in the rapidly developing
field of `quantum batteries'.
