Despite all the advances made, cancer continues to be one of the main pathologies, responsible for almost ten million deaths worldwide in 2020, being lung cancer, colon cancer, liver cancer, stomach cancer, and breast cancer the main five neoplasms responsible for these deaths. In all these tumors, chemotherapy is one of the main therapeutic strategies, especially in advanced stages of the disease and when tumor cells have invaded other tissues and have metastasized. However, current antineoplastics are, in general, highly toxic which limits their dose and, therefore, their efficacy. In addition, many are poorly soluble in water, making them difficult to administer and requiring the use of organic solubilizing agents which increase the toxicity. In this sense, the use of nanocarriers can solve these problems and improve conventional chemotherapeutic treatments. On the one hand, these systems, in general, reduce the toxicity of these antineoplastics, since they tend to accumulate in the tumors, limiting the access of free drug to other tissues which allow the administration of higher doses. In addition, they allow the administration of very lipid-soluble antineoplastics without using these solubilizing agents. On the other hand, due to this selective accumulation, greater efficiency could also be obtained. This chapter discusses the nanoformulations that are currently approved or under clinical research for the treament of the main life-threatening tumors, indicating their advantages and disadvantages over conventional treatments, and underlying challenges of their clinical translation.