This contribution illustrates the potential of nitrogen-rich by-products and waste streams as sources for proteins and amino acids. Furthermore, applications of recovered nitrogen compounds in food and feed as well as non-food and non-feed products have been illuminated. It has been shown that, for instance, cheese, yoghurt, and whey have essential amino acid content above 40% (w/w) of the total amino acid pool. Pumpkin seed pie, hops and sea buckthorn seeds, although the protein content can be more than 20% (w/w) crude protein in dry matter, show a rather poor essential amino acid profile. It should be admitted here that even streams containing diluted amounts of nitrogen compounds such as wastewater should be used. This, however, may only be economically feasible when prior recovery a concentration step is carried out. To foster the recovery and utilization of nitrogen compounds, this contribution describes the challenges and chances of current approaches.