This collection features five peer-reviewed reviews on dietary supplements in poultry nutrition. The first chapter reviews latest research on feed enzymes focussing on identifying the key challenges researchers face in terms of current trends in enzyme development, mechanism(s) of action and enzyme efficacy. The second chapter considers the role of probiotics in optimising gut function in poultry. It reviews the development of novel, cost-effective, feed-stable, direct-fed microbials with potential for widespread utilisation and improved production. The third chapter discusses the role of essential oils and botanicals in improving gut function in poultry, focussing on four major functions of phytobiotics that could potentially contribute to gut health: digestive conditioning, antimicrobial property, immunomodulation and gut microbiota modulation. The fourth chapter considers the development of alternative protein sources for poultry nutrition, including grain by-products, pulses and algae. It also reviews best practices for improving the nutritive value of these alternative protein sources. The final chapter reviews the effects of supplemental full- or de-fatted microalgal biomass in poultry diets on animal production and performance, meat and egg qualities, as well as nutrient metabolism and molecular responses.