The present disclosure is drawn to non-aqueous ink compositions. The non-aqueous ink compositions can include from 70 wt % to 98 wt % alcohol solvent, from 1 wt % to 6 wt % phenol-formaldehyde resin, from 1 wt % to 5 wt % tackifier, and from 1 wt % to 14 wt % organic solvent-soluble dye. The tackifier can include a shellac having an acid number from 50 KOH/g to 100 mg KOH/g or a tackifier resin having an acid number from 100 mg KOH/g to 300 mg KOH/g.