A theoretical force field for the ground-state vibrations of nonionized glycine $H_2NCH_2COOH$ has been determined from ab initio calculations at the Hartree-Fock level with 4-21G basis set. The experimental infrared spectra of $H_2NCH_2COOH, H_2NCD_2COOH$, $^{15}NH_2CH_2COOH, H_2NCH_2C^{18}O^{18}OH$, and their nitrogen- and oxygen-deuterated isotopomers observed from the matrix-isolated species have been assigned with the aid of the potential energy distributions calculated for each of the normal modes using the theor. force field. The calculated isotopic frequency shifts for $^{15}N, ^{18}O$, and $^2H$ substituted glycines are also found to be in close agreement with the experimental isotopic frequency shifts. The calculated infrared band intensity pattern shows good agreement with the experimental spectrum of glycine. From a complete assignment of the vibrational fundamentals observed from the infrared spectra of glycine and its several isotopic molecules, a stretched framework planar conformer is concluded to be the more stable form, reconfirming the results of the other studies on nonionized glycine.