Cancer causes the second highest mortality rate after the cardiac diseases in humans. In addition to death rates, cancer morbidity paints a rather grim picture. Despite the advances in treatment modalities, cancer management still remains as a challenging task. In vitro biological evaluations use cytotoxicity as one of the most essential indications. In vitro, cytotoxic drugs cause cell membrane disintegration, protein synthesis inhibition, and irreversible receptor binding, among other things. To identify cell death caused by these insults, a number of short-term cytotoxic effects and cell proliferation assays have been developed and employed. Chemical carcinogenesis and xenograft models for imitating human malignancies are among the in vivo models that have been developed. This article discusses the current in-vitro and animal models used in the discovery and therapeutic efficacy assessment of anti-cancer drugs.