Sustainable ammonia or green ammonia is ammonia synthesized using renewable energy, nitrogen and water. The road to sustainable ammonia has been described as a transition of generations of technology. Brown ammonia is the current form of industrially produced ammonia via steam reforming and the H-B process. Blue ammonia, or low-carbon ammonia, is the result of brown ammonia with carbon capture and storage technology applied during manufacturing processes. Green ammonia is defined as zero-carbon ammonia, made using sustainable electricity, water and air. Green ammonia synthesis has been proposed to first take place by substituting steam reforming of methane with green hydrogen generated from green energy-powered electrolysis of water. Application of the green hydrogen into a H-B process powered by renewable energy would generate green ammonia and zero carbon. An additional stage of green ammonia is the direct catalyzed synthesis of ammonia from water and nitrogen powered by renewable energy. This proposed process of direct reduction of nitrogen with water and electricity would be ideal for distributed ammonia generation; meaning that ammonia could be directly generated at the farm without the need of transportation or large-scale industrial equipment. To date, catalysts have only been shown to be capable of low rates of ammonia production and only in laboratory scale synthesis. New electrocatalysts, electrolytes and systems must be developed that can produce ammonia in preference to hydrogen and achieve competitive production rates. However, this field has progressed quickly over the last 10-20 years and with con nuous rigorous experimentation, a viable system may not be far off.