The photoelectron (PE) spectra of cyclopentadiene (CP) and its perdeuterated isotopomer (CP-d(6)) and the electronic absorption (EA) and infrared (IR) spectra of the corresponding radical cations are presented. The electronic structure of CP.+ is discussed on the basis of CASSCF/CASPT2 calculations which reproduce the excited-state energies as derived from the PE and EA spectra very well. Density functional force fields are scaled to fit the observed bands in the IR spectra and vibrational progressions in the first PE bands. The changes in valence force constants upon ionization of CP are discussed on the basis of qualitative expectations and compared to those found earlier for butadiene.