Ammonia is considered a key energy carrier with potential applications for low carbon energy storage, transportation and power generation. This carbon-free molecule offers several advantages, including high energy density and a wide and well-established production and distribution infrastructure that have been optimized for over a century. In this perspective, we analyze the potential roles of ammonia as an energy carrier, and summarize research areas requiring further development for the implementation of ammonia as a building block in the global sustainable energy landscape. Ammonia technologies are reviewed with an emphasis on current limitations and recent advances. Focus is placed on available technologies for ammonia synthesis, decomposition into CO_x-free hydrogen and direct use of ammonia for power generation and transportation.