Feed resource efficiency contributes to sustainable production of pig meat, both economically and environmentally. This chapter describes different measures of feed efficiency and the underlying genetics of feeding in pigs, drawing on studies of genetic correlations of residual feed intake (RFI) with pig production traits and genome-wide association studies (GWAS) revealing the genetic architecture and biological mechanisms of feed efficiency. The chapter looks ahead to the future and recommends adoption of an integrative systems genomic approach to ensure accurate genomic prediction and a more comprehensive biological understanding of feed efficiency.