  With much advancement in the field of nanotechnology, bioengineering and
synthetic biology over the past decade, microscales and nanoscales devices are
becoming a reality. Yet the problem of engineering a reliable communication
system between tiny devices is still an open problem. At the same time, despite
the prevalence of radio communication, there are still areas where traditional
electromagnetic waves find it difficult or expensive to reach. Points of
interest in industry, cities, and medical applications often lie in embedded
and entrenched areas, accessible only by ventricles at scales too small for
conventional radio waves and microwaves, or they are located in such a way that
directional high frequency systems are ineffective. Inspired by nature, one
solution to these problems is molecular communication (MC), where chemical
signals are used to transfer information. Although biologists have studied MC
for decades, it has only been researched for roughly 10 year from a
communication engineering lens. Significant number of papers have been
published to date, but owing to the need for interdisciplinary work, much of
the results are preliminary. In this paper, the recent advancements in the
field of MC engineering are highlighted. First, the biological, chemical, and
physical processes used by an MC system are discussed. This includes different
components of the MC transmitter and receiver, as well as the propagation and
transport mechanisms. Then, a comprehensive survey of some of the recent works
on MC through a communication engineering lens is provided. The paper ends with
a technology readiness analysis of MC and future research directions.
