Animal-based agriculture and the production of protein-rich foods from animals, particularly from ruminants, is not sustainable and has serious climate effects. A new type of alternative proteins is now on the menu, namely animal proteins produced recombinantly by microbial fermentation. This new technology, precision fermentation, is projected to completely disrupt traditional animal-based agriculture. Certain milk and egg proteins along with specific meat substitute analog components produced by precision fermentation are already entering the market. This first wave of precision fermentation products targets the use of these proteins as protein additives, and several commercial players are already active in the field. The cost-efficiency requirements involve production titers above 50 g/L which are several orders of magnitude higher than those for pharmaceutical protein manufacture, making strain engineering, process optimization, and scale-up critical success factors. This new development within alternative proteins defines a new research direction integrating biotechnology, process engineering, and sustainable food protein production. Expected final online publication date for the Annual Review of Food Science and Technology, Volume 15 is April 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.