Fluorescent chemosensors are highly valuable in a variety of fields including environmental chemistry, analytical chemistry, and bio-medicinal science. They have provided accurate, on-line, and low-cost detection of toxic heavy metal ions, anions, and enzymes with high selectivity and sensitivity. Coumarins, with the structure of benzopyrone, have many advantages including high fluorescence quantum yield, large Stokes shift, excellent light stability, and less toxicity. Therefore coumarins have been widely used in the fields of biology, medicine, perfumes, cosmetics, and fluorescent dyes. By far coumarin derivatives have been used as fluorescent probes of pH, for detection of nitric oxide, nitroxide, and hydrogen peroxide. Moreover, coumarin derivatives have served as good chemosensors of anions including cyanide, fluoride, pyrophosphate, acetate, benzoate, and dihydrogenphosphate as well as various metal ions comprised of Hg(II), Cu(II), Zn(II), Ni(II), Ca(II), Pb(II), Mg(II), Fe(III), Al(III), Cr(III), and Ag(I). Several systems containing coumarin exhibited simultaneous sensitivity toward two or more different metal ions, e.g. Ca(II) and Mg(II), Ni(II) and Co(II), Cu(II) and Hg(II), Na(I) and K(I), Cu(II) and Ni(II), Hg(II) and Ag(I), Cu(II)/Ni(II)/Cd(II), Zn(II)/Cd(II)/Pb(II), or Ni(II)/Pd(II)/Ag(I). Herein a brief review of fluorescent chemical sensors derived from coumarins is presented.