[en] A resume is given of the experimental data on energy levels of isolated actinide neutral atoms and ions derived from analysis of the spectra of the vapour phase at low density. Typically, a neutral actinide has a thousand experimental levels and the ionized state somewhat fewer. Most levels can be identified only by comparison with theoretical calculations using appropriate parameters. The theoretical description of the term structure is outlined and the fitting of parameters discussed. The lowest level of all known actinide electron configurations is listed together with isotope shifts and hyperfine structure widths. Some interpretation of the data in terms of general trends and the implications for actinide chemistry is attempted. (author)