Results of theoretical description of the reactions of concerted molecular decomposition of alkyl halides RX to olefin and HX have been analyzed. Data on quantum-chemical calculation of the transition state of these reactions are given. The results obtained by analyzing experimental data in terms of the model of intersecting parabolas have been compared. The following factors determining the reactivity of RX (X = F, Cl, Br, I) in the decomposition reactions: enthalpy of decomposition, force constants of reacting bonds, triplet repulsion, electronegativity of the reaction-center atoms, the pi-bond adjacent to the reaction center, dipole-dipole interaction, and elongation of the R-X bond win the transition state, have been distinguished. The energy spectrum of partial activation energies of the concerted molecular degradation of RX has been constructed.