The Fanconi anemia ID complex consists of two subunits, Fanconi anemia I and Fanconi anemia D2 (FANCI-FANCD2) and plays a central role in the repair of DNA interstrand cross-links (ICLs). The complex is activated via DNA damage-induced phosphorylation by ATR (ataxia telangiectasia and Rad3-related) and monoubiquitination by the FA core complex ubiquitin ligase, and it binds to DNA at the ICL site, recognizing branched DNA structures. Defects in the complex cause Fanconi anemia, a cancer predisposition syndrome. The phosphorylation of FANCD2 is required for DNA damage-induced intra-S phase checkpoint and for cellular resistance to DNA crosslinking agents.