Lithium (Li) is a fragile material, easily destroyed in stellar interiors. Within our current understanding of stellar evolution for stars more massive than $\sim6\:$M$_{\odot}$, Li should be depleted in the atmospheres of all such stars well before the time when they reach the He core burning phase. Despite this prediction, we find a high fraction of red supergiants (RSGs), i.e. He-core burning massive stars with convective envelopes, displaying moderate to strong Li I 6708Å doublet lines. Based on a large sample of Perseus arm RSGs, about one third of Milky Way supergiants contain measurable amounts of lithium. For the Magellanic Cloud, relatively small samples point in very different directions. In the LMC, the fraction is at least as high as that of the Milky Way. Contrarily, in the SMC, the fraction seems to be much smaller. These observational results may hint at either a Li production mechanism in RSGs or the widespread engulfment of substellar companions. Further characterisation work is ongoing, while theoretical studies into this matter are urgently needed.