In polarized infrared (IR) absorption experiments, dichroic values are used to study the structure and orientation of lipid molecules. From computer simulations, we obtained angular distributions of IR transition moment (TM) orientations of the stretch vibrations of CH 2 groups of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholin (POPC) lipid bilayers in the gel (L/~) and fluid (L a) phases. From these distributions, we calculated dichroic absorption values, as well as order parameters. We established a connection between the dichroic ratio R am, which is measured in IR-ATR setups, with the dichroic ratio D and the order parameter Szz.The calculated values compare well with experimental results for the fluid phase. In addition, we computed angular distributions of transition moments with respect to the tail director orientation for the gel and the fluid phases. Only small differences were found between the distributions in the symmetric stretch orientation, the asymmetric stretch orientation, and the C-H bond orientation of CH 2 groups. The distributions of tail directors of POPC showed average tilts of 14.7 ° in the gel phase and 32.9 ° in the fluid phase. We developed a theory which makes it possible to calculate average tilt angles of tail directors in the gel phase from dichroic absorption values obtained from IR measurements for a wide range of lipids. Legendre coefficients were calculated from TM distributions. Order parameters, defined as the second Legendre polynomial, were found to closely approximate the TM distribution in lipid bilayers in the fluid phase.