Nuclear fusion research, using magnetically confined plasmas, needs a great amount of atomic data in the fields of plasma diagnostics, plasma spectroscopy and modelling. Conventional spectroscopy and some specialised techniques are being used for analysing plasma behavior and plasma composition. Hydrogen data are required, as well as coefficients for impurities originating from the vacuum vessel walls and protection tiles. Some noble gases are being used for radiative cooling or transport studies of highly ionized ions. For measuring metal concentrations, diagnostic lines from the plasma interior are recorded, sometimes of highly ionized species like Zn-like tungsten. The ionization balance and the emitting shells must be calculated on the basis of the relevant atomic data and of the transport coefficients. For high heat-load areas, carbon is mostly used at present, which is fully ionized in the plasma and can only be measured by charge-exchange recombination spectroscopy. Impurity particle influxes at the boundary are derived from lines of neutrals or low ionization stages, a method, which can also be extended to the band emission of molecules. In this way, chemical erosion of carbon is being investigated. In cold divertor plasmas, hydrogen molecules also play some role, e.g. enhancing hydrogen ion recombination. In addition to the usual coefficients for ionization, recombination, charge exchange and radiation for all relevant elements, molecular data are required in model calculations of the plasma boundary and of divertors. Some examples of interpretation methods and experimental results in these fields are presented. ©2000 American Institute of Physics.