We describe the direct synthesis of organophosphorus compounds from ubiquitous aryl and vinyl carboxylic acids via decarbonylative palladium catalysis. The catalytic system shows excellent scope and tolerates a wide range of functional groups (>50 examples). The utility of this powerful methodology is highlighted in the late-stage derivatization directly exploiting the presence of the prevalent carboxylic acid functional group. DFT studies provided insight into the origin of high bond activation selectivity and P(O)-H isomerization pathway.