Genome editing technologies such as clustered regularly interspaced short palindromic repeats (CRISPR) systems have ushered in a new era of targeted DNA manipulation. The easy programmability of CRISPR using short oligonucleotides enables rapid synthesis of large-scale libraries for functional genetic screens. Here we present fundamental concepts and methods for pooled CRISPR screens and review biological results from recent genome-scale loss-of-function and gain-of-function screens. We also discuss new frontiers in pooled screens, including novel effector domains for functional screens and applications in the noncoding genome.