The Chordates are animals that comprise the phylum Chordata. Taxonomically the phylum Chordata includes three subphyla: Tunicata; Cephalochordata, comprising the lancelets; and the Craniata, or Vertebrata. The common attributes of the Chordata include having, for at least some period of their life cycles, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail. The phylum Hemichordata has been presented as a fourth chordate subphylum, but it now is usually treated as a separate phylum.

Tunicate larvae have both a notochord and a nerve cord which are lost in adulthood. Cephalochordates have a notochord and a nerve cord (but no brain or specialist sensory organs) and a very simple circulatory system. Craniates are the only subphylum whose members have skulls. In all craniates except for hagfish, the dorsal hollow nerve cord is surrounded with cartilaginous or bony vertebrae and the notochord is generally reduced; hence, hagfish are not universally regarded as vertebrates, though recent DNA comparisons suggest that they are in fact vertebrates. The chordates and three sister phyla, the Hemichordata, the Echinodermata and the Xenoturbellida, make up the deuterostomes, one of the two superphyla that encompass all fairly complex animals.