A combined experimental and theoretical approach has been used to investigate X−$\cdots$CH2O (X=F, Cl, Br, I) complexes in the gas phase. Photoelectron spectroscopy, in tandem with time-of-flight mass spectrometry, has been used to determine electron binding energies for the Cl−$\cdots$CH2O, Br−$\cdots$CH2O, and I−$\cdots$CH2O species. Additionally, high-level CCSD(T) calculations found a C2v minimum for these three anion complexes, with predicted electron detachment energies in excellent agreement with the experimental photoelectron spectra. F−$\cdots$CH2O was also studied theoretically, with a Cs hydrogen-bonded complex found to be the global minimum. Calculations extended to neutral X$\cdots$CH2O complexes, with the results of potential interest to atmospheric CH2O chemistry.