<p>Processed animal proteins (PAPs) are concentrated protein ingredients derived from animal by-products through rendering or hydrolytic processes and are increasingly reconsidered in poultry nutrition due to their nutritional and sustainability advantages. This review provides a comprehensive evaluation of the composition, digestibility, functional properties, safety, and practical applications of PAPs in poultry feeding systems. Nutritional value varies considerably depending on raw material origin and processing conditions, with excessive heat treatment reducing amino acid availability through Maillard reactions and racemization. Blood-derived products and spray-dried plasma exhibit high digestibility and functional benefits, particularly in early-life feeding, whereas hydrolyzed feather meal and poultry by-product meal show variable performance depending on processing quality and inclusion levels. Emerging sources such as insect meals and fermented protein hydrolysates offer promising alternatives but require standardization to ensure consistent nutritional value and safety. Digestibility assessment methods differ substantially, and comparisons across studies require careful interpretation to avoid misleading conclusions. Production trials indicate that partial replacement of soybean meal with non-ruminant PAPs can maintain or improve growth performance, gut health, and nutrient efficiency when diets are formulated on a digestible amino acid basis. Safety considerations, including microbial hazards, chemical residues, and regulatory compliance, remain critical and are supported by advances in analytical detection technologies. Overall, PAPs represent a viable and sustainable protein source in poultry nutrition, provided that processing, quality control, and formulation strategies are carefully managed.</p>