Proteins have a wide range of functions, including muscle development, tissue repair, the execution of metabolic reactions, the activities of the immune system, and the transport of substances within the body. Proteins are sourced from two main types: animal-based and plant-based. Animal-based foods with high protein content include meat, fish, eggs, milk, and dairy products. Plant-based protein sources are primarily cereals, legumes, and nuts. Each animal product contains all the essential amino acids crucial for human nutrition. In contrast, plant sources have these amino acids in varying amounts, necessitating a diverse diet of plant products to consume all essential amino acids. Plants, the fundamental elements of the biosystem, rush to aid animals, who in turn help meet the food needs of humans, showcasing the principle of mutual assistance in the world. Foods needed by both humans and animals have been integrated into plants by the Governor of the universe. The increase in the consumption of processed ready-made foods in industrial societies and the resulting rise in diseases have led people to prefer more natural, unprocessed plant and animal foods. Recently, the challenge in meeting the protein needs of both animals and humans has prompted policymakers and researchers to seek economic and sustainable protein sources. Particularly, global climate change and its resulting fluctuations in plant production cause variations in the availability of alternative sources. The insufficiency and high cost of animal protein sources encourage people to consume inexpensive plant-based products rich in protein, such as legumes. The book, discussing the unique advantages of alternative protein sources, technological possibilities, and potential future risks in food supply, offers alternative solutions and comprises 11 chapters. Therefore, we are pleased to present to you valuable readers the original, review, and evaluation studies prepared by experts in the field on both plant and animal protein sources.