<p>Unlike normal cells, which primarily rely on oxidative phosphorylation, cancer cells reprogram their metabolism by preferentially utilizing glycolysis even in the presence of oxygen to generate ATP. As a result, cancer cells and the tumor microenvironment typically accumulate high levels of lactate. Although initially considered a mere byproduct of glucose metabolism, lactate has recently emerged as an important metabolic intermediate involved in many intracellular pathways and protein modifications. Lysine lactylation is indeed a newly identified, metabolism-linked post-translational modification in which lactate is covalently bound to specific lysine residues. This review provides an overview of the current understanding of how lysine lactylation mechanistically contributes to therapeutic resistance in tumor cells. Remarkably, protein lactylation is emerging as a promising druggable approach for overcoming therapy resistance. Hence, here, we also highlight new strategies that target lactylation with pharmacological inhibitors to counteract drug resistance in cancer.</p>