The reactions of ground state yttrium atoms (Y) with formaldehyde (H2CO) have been studied in crossed molecular beams as a function of collision energy (E-coll). The potential energy barrier for C-H insertion is found to lie below 12 kcal/mol. It is proposed that the reaction is initiated by C-H insertion, producing HYCHO followed by H atom migration forming H2YCO. Although Y-CO bond fission leading to YH2+CO is dominant, a secondary minor channel also leads to the production of YCO+H-2. Formation of YCHO+H is not observed at 16 kcal/mol, but is clearly seen at 31 kcal/mol, indicating that D-0(Y-CHO) lies between 58 and 73 kcal/mol.