The available data on the microwave spectra of formaldehyde, formamide, and thioformaldehyde are critically reviewed for information applicable to radio astronomy. Molecular data such as rotational constants, centrifugal distortion parameters, dipole moments, hyperfine coupling constants, and structural parameters are tabulated. Observed rotational transitions are presented for the astronomically interesting isotopic forms of these molecules when available. Detailed centrifugal distortion calculations have been carried out for the most abundant isotopic forms of these molecules, namely, H212C16O, H213C16O, 14NH212CH16O, and H212C32S. Transitions have been predicted and tabulated for the frequency ranges 1 MHz to 300 GHz for H212C16O,100 MHz to 300 GHz for H213C16O,500 MHz to 180 GHz for 14NH212CH16O,100 MHz to 300 GHz for H212C32S. All predicted transitions include 95 percent confidence limits; measured transition error limits have been reproduced from the original literature. References are given for all data included.