We thoroughly and critically review studies reporting the real (refractive index) and imaginary (absorption index) parts of the complex refractive index of silica glass over the spectral range from $30\mathrm{nm}$ to $1000\mu \text{m}$. The general features of the optical constants over the electromagnetic spectrum are relatively consistent throughout the literature. In particular, silica glass is effectively opaque for wavelengths shorter than $200\mathrm{nm}$ and larger than $3.5–4.0\mu \text{m}$. Strong absorption bands are observed (i) below $160\mathrm{nm}$ due to the interaction with electrons, absorption by impurities, and the presence of OH groups and point defects; (ii) at $\sim 2.73–2.85$, 3.5, and $4.3\mu \text{m}$ also caused by OH groups; and (iii) at $\sim 9–9.5$, 12.5, and $21–23\mu \text{m}$ due to Si―O―Si resonance modes of vibration. However, the actual values of the refractive and absorption indices can vary significantly due to the glass manufacturing process, crystallinity, wavelength, and temperature and to the presence of impurities, point defects, inclusions, and bubbles, as well as to the experimental uncertainties and approximations in the retrieval methods. Moreover, new formulas providing comprehensive approximations of the optical properties of silica glass are proposed between 7 and $50\mu \text{m}$. These formulas are consistent with experimental data and substantially extend the spectral range of $0.21–7\mu \text{m}$ covered by existing formulas and can be used in various engineering applications.