Soft X-ray spectroscopic diagnostics of laboratory plasmas are considered. To start with, the state of the art in the knowledge of rate coefficients, cross-sections, transition probabilities, and ionization equilibrium calculations is reviewed. Next, the plasma spectral emission, i.e. continuum and line emission (including satellites), line broadening (including opacity), and total emitted radiation as an energy loss process, is considered. To conclude, a short discussion of X-ray plasma sources and instrumental problems is presented.