Drug resistance is a major obstacle in cancer therapy. To elucidate the genetic factors that regulate sensitivity to anti-cancer drugs, we performed CRISPR/Cas9 knockout screens for resistance to a spectrum of drugs. In addition to known drug targets and resistance mechanisms, this study revealed novel insights into drug mechanisms of action, including cellular transporters, drug target effectors, and genes involved in target-relevant pathways. Importantly, we identified 41 multi-drug resistance genes, including an uncharacterised gene. Thisuncharaterised gene is therefore required for drug-induced death (RDD1) and has been named here as such. Low RDD1 expression was associated with poor prognosis in multiple cancers and characterisation of the resulting protein reveals potential cell cycle-dependent mechanisms by its association to mitotic components. Together, we provide the first functional landscape of resistance mechanisms to a broad range of chemotherapeutic drugs and reveal new multi-drug resistance nodes. This information can guide personalised therapies or instruct rational drug combinations to minimise acquisition of resistance.