  We describe the atomic and molecular data that were used for the abundance
analyses of FGK-type stars carried out within the Gaia-ESO Survey. We present
an unprecedented effort to create a homogeneous line list, which was used by
several abundance analysis groups to calculate synthetic spectra and equivalent
widths. The atomic data are accompanied by quality indicators and detailed
references to the sources. The atomic and molecular data are made publicly
available in electronic form. In general experimental transition probabilities
were preferred but theoretical values were also used. Astrophysical gf-values
were avoided due to the model-dependence of such a procedure. For elements
whose lines are significantly affected by hyperfine structure or isotopic
splitting a concerted effort has been made to collate the necessary data for
the individual line components. We also performed a detailed investigation of
available data for line broadening due to collisions with neutral hydrogen
atoms. Synthetic spectra calculated for the Sun and Arcturus were used to
assess the blending properties of the lines. Among a subset of over 1300 lines
of 35 elements in the wavelength ranges from 475 nm to 685 nm and from 850 nm
to 895 nm we identified about 200 lines of 24 species which have accurate
gf-values and are free of blends in the spectra of the Sun and Arcturus. For
the broadening due to collisions with neutral hydrogen we recommend data based
on Anstee-Barklem-O'Mara theory, where available, and to avoid lines of neutral
species otherwise. Theoretical broadening data by R.L. Kurucz should be used
for Sc II, Ti II, and Y II lines. For ionised rare-earth species the Uns\"old
approximation with an enhancement factor of 1.5 for the line width can be used.
Desirable improvements in atomic data were identified for a number of species,
including Al I, S I, Cr II, Na I, Si I, Ca II, and Ni I.
