We report the discovery of the rotational spectrum of CH+ in the Infrared Space Observatory Long Wavelength Spectrometer (LWS) spectrum of the planetary nebula NGC 7027. The identification relies on a 1996 reanalysis of the LWS spectrum by Liu et al. and on new LWS data. The strong line at 179.62 μ m (coinciding with the 2 12–1 01 transition of water vapor) and the lines at 119.90 and 90.03 μ m (reported as unidentified by Liu et al.), whose frequencies are in the harmonic relation 2: 3: 4, are shown to arise from the J= 2–1, 3–2, and 4–3 rotational transitions of CH+. This identification is strengthened by the new LWS spectra of NGC 7027, which clearly show the next two rotational lines of CH+ at 72.140 and 60.247 μ m. This is the first time that the pure rotational spectrum of CH+ has been observed. This discovery opens the possibility of probing the densest and warmest zones of photodissociation regions. We derive a rotational temperature for the CH+ lines of 150�20 K and a CH+ &solm0; CO abundance ratio of 2–6� 10-4.