We have developed the stereoselective Horner–Wadsworth–Emmons (HWE) reaction of aldehydes with 2-fluoro-2-diethylphosphonoacetic acid (1) employing i-PrMgBr for the synthesis of (Z)-α-fluoro-α,β-unsaturated carboxylic acids as the major products. (E)-α,β-unsaturated carboxylic acids were obtained by the HWE reactions of aryl alkyl ketones with bis(2,2,2-trifluoroethyl)phosphonoacetic acid (2) utilizing lithium hexamethyldisilazide in N,N-dimethylformamide. Phosphonoacetic acid 2 was prepared by enzymatic hydrolysis of the corresponding methyl ester with porcine liver esterase (PLE). In addition, a novel P-chiral HWE reagent was synthesized by the PLE-promoted kinetic resolution of racemic phosphonates.