We report a combined experimental and theoretical study of the low-lying electronic states of cyclopentadienone (C5H4O). The cyclopentadienone anion (C5H4O-) was generated in the gas phase via reaction of atomic oxygen radical anions (O-) with cyclopentanone (C5H8O). Photoelectron imaging was used to gain access to the first three electronic states of C5H4O, including the X(1)A(1) ground state and the B-3(2) and (3)A(2) excited states. The first two state assignments are supported by the Franck-Condon simulations of the vibrational progressions observed in the X (1)A(1), and B-3(2) bands in the photoelectron spectra. The adiabatic electron affinity of cyclopentadienone in the ground state is determined to be EA(X (1)A(1)) = 1.06 +/- 0.01 eV, and the corresponding values for the first two excited states are EA(B-3(2)) = 2.56 +/- 0.02 eV and EA((3)A(2)) = 3.45 +/- 0.01 eV. These experimental determinations are in excellent agreement with the CCSD(T) theory predictions, lending further confidence to the above state assignments. On the basis of these results, the lowest singlet-triplet splitting (between the X (1)A(1) and B-3(2) states) in cydopentadienone is Delta ES-T = 1.50 +/- 0.02 eV.