Extraordinary physics of carbon nanotubes (CNTs) positions them among most popular objects studied by modern condensed matter physicists. The novel fundamental properties of CNTs are highly attractive for possible practical applications in nano- and macro-electronics. In the latter case, centimeters-size thin layers or films composed by large amount of CNTs, disordered or aligned, can be regarded as either separate “devices” (for example, polarizers of terahertz radiation) or as components of more complex schemes and constructions. However, presently, the issues of microscopic mechanisms of charge transport and of low-energy electrodynamics of the two-dimensional arrays of CNTs are basically open: the existing experimental data are often inconsistent, sometimes even controversial, and their interpretations ambiguous or even conflicting. We have measured terahertz-infrared spectra of optical conductivity and dielectric permittivity of high-quality pristine and doped (with CuCl and iodine) SWCNT films, at frequencies from 7 cm^-1 up to 24 000 cm^-1 and in a broad temperature interval, from 300 K down to 5 K. We find that the spectra demonstrate typical metallic frequency and temperature behaviors and can be described using the Drude conductivity formalism. We determine the temperature dependences of effective parameters of free charge carriers within the films that characterize the films’ terahertz-infrared response: the plasma frequency, the scattering rate, the mobility. Additionally, in pristine films, clear signatures are detected of the tunnel gap that governs the dc and the ac transport at low temperatures (below 100-150 K). Our experiments clearly demonstrate that the terahertz-infrared spectroscopy is an effective technique to study transport mechanisms in carbon nanotube layers.