Recently there has been an exciting conflict on the optical band gap of InN. The determination of the band gap energy of amorphous (a) InN thin film presented a challenge and added another dimension to the Eg conflict. At temperature < 325 K, we deposited InN thin films onto different substrates (c-Si (111), glass, and quartz) by using RF magnetron sputtering at a rate between 0.03 and 0.04 nm/s. X-ray diffraction patterns revealed that the films grown on the substrates have an amorphous nature over a wide range of diffraction angles (20o- 100o). The optical Eg of a-InN have been determined by three independent methods, spectroscopic ellipsometry (SE), spectrophotometric (SP), and photoluminescence (PL) over the energy range 0.88 - 4.1 eV. The absorption coefficient, α, was obtained by the analysis of the measured ellipsometric spectra through the Tauc-Lorentz model. The optical bandgap was determined using the modified Tauc and Cody extrapolations. The corresponding Tauc and Cody optical bandgaps were found to be 1.73 and 1.72 eV, respectively. These values were in excellent agreement with the values of the bandgap energy obtained as fitting parameters in the Tauc-Lorentz model: 1.72 ± 5.9 × 10-3 eV. Using the SP method, α was calculated according to the Beer-Lambert law and it showed that the value of the bandgap (1.74 eV) was much closer to that by the analysis of SE data, and also to the values of Eg as a fitting parameter in the chosen model. The PL spectra of the films showed only one strong band edge at 1.69 eV while it exhibited only one weak band edge PL emission at 1.63 eV. The spectral dependence of the polarized absorptivities was investigated at different angles of incidence. We found that there was a higher absorptivity for wavelength < 725 nm. This wavelength, ~ 725 nm, therefore indicated that the absorption edge for a-InN film is about 1.70 eV.