Feed utilization efficiency is a trait of high economic importance in livestock production. In poultry meat and egg production, feed accounts for over 70% of the total production costs. Consequently, improving feed utilization efficiency has been a major goal in the poultry industry. The efficient use of feed for livestock production also positively impacts environment. After a brief history of broiler breeding, this chapter summarizes the quantitative genetic properties (heritability and genetic correlation estimates) of feed efficiency and discusses some of its main contributing factors: basal metabolism, protein turnover, body composition, and digestive efficiency. Contribution of metabolic systems (liver, adipose tissue and skeletal muscle) and relevant genomic studies are also discussed. The chapter also includes a section on unfavorable meat quality consequences of improving feed efficiency and ends with discussion on future considerations.