Four bands in the infrared spectrum of ethylene-H 4 are studied with a resolution of 0.03 - 0.04 cm -1, the A-type ν11 fundamental, the B-type ν9 fundamental, and the B-type ν5 + ν12 and ν6 + ν11 combination bands. From ∼300 combination differences, the following ground-state rotational constants are determined: A0 = 4.86596 ± 0.00018, B0 = 1.001329 ± 0.000061, C0 = 0.828424 ± 0.000062, D J0 = 1.447 ± 0.070 × 10 -6, D JK0 = 1.468 ± 0.063 × 10 -5, D K0 = 9.17 ± 0.16 × 10 -5cm-1. Upper-state rotational constants are reported for all four bands, some Coriolis interactions are identified, and the relevant ξ constants are determined. The value of the band center of ν5 + ν12 leads to a suggested reassignment of Q branches in the Raman active fundamental ν5, and a revision of the band center to 3086 cm -1. The new data for C 2H 4 determined in this work are summarized in Table VII, along with all the other currently available data on the vibrational and rotational constants.