Molecular communications (MC) is an emerging field, inspired by nature (e.g., endocrine signaling), that aims to use molecules to encode information. MC is attracting increasing attention as an unconventional solution to challenges posed in environments where conventional electromagnetic-based communication is not feasible or detrimental, such as inside the human body. MC is rapidly becoming a powerful tool that has the potential to drive transformative applications in chemistry, biology and medicine, and identified a key enabling communication method for the Internet of Bio-Nano Things (IoBNT). Due to the focus on energy efficiency and bio-compatibility it paves the way for efficient and reliable communication at micro- and nanoscale.