Plasma-assisted ammonia (NH3) synthesis is receiving significant attention·NH3 is globally important to fertilizer production and as a fuel. However, plasma research is, intrinsically, significantly cross-disciplinary and encompasses chemistry, physics, materials science and electrical engineering. A consequence is that it is uncommon for plasma researchers to be fully aware of the entirety of plasma-related research beyond a particular discipline. Here for the first time we critically review this cross-disciplinary literature to address this problem using plasma-enabled NH3 synthesis as an eminent showcase for process chemistry. A justification is that an improved understanding will be helpful to deal with the complexity of plasma processes which typically involve a set of chemical reactions with an ensemble of many short-lived excited, or reactive, species that vary amongst different plasmas. In this way, mechanisms for plasma-driven NH3 synthesis are deciphered which helps to improve plasma reaction engineering. Modern analytical techniques are critical in deciphering these fundamentals and in this review optical emission spectroscopy (OES) is featured.