The chapter examines and analyses scientific publications devoted to the role of mitochondria in the support of the life of transformed cells and to the study of the characteristics and structural and functional dysfunctions of mitochondria. Issues of the mitochondrial control of cellular redox homeostasis and sites of mitochondrial reactive oxygen species (ROS) production in the inner mitochondrial membrane are considered. The features of the structural and functional reorganisation of mitochondria in malignant tumour cells and the mechanisms of reprogramming energy metabolism, increasing ROS production, and adaptation to the conditions of hypoxia and metabolic stress are analysed. Mitochondrial dysfunction, activation of oncogenes, inactivation of anti-oncogenes, and the tumour cell microenvironment have a profound effect on the metabolism of cancer cells and determine the heterogeneity of metabolic profiles between different tumour types. The importance of identifying specific metabolic changes in each malignant tumour is clear given the need to effectively influence its growth. Understanding the role of mitochondrial dysfunction is very important for studying the pathophysiology of cancer and many other common diseases. This gives impetus to the development of mitochondrial pharmacology using mitochondria as targets for different types of effects, which can serve as the biochemical basis for the development of new antitumour agents. Perhaps the combined use of mitochondrial metabolism modulators and antitumour agents will contribute to the emergence of a new direction in antitumour therapy that will significantly increase the effectiveness of treatment for cancer patients.