This text attempts to provide a clear and straightforward account of the biochemistry underlying the physiological functions of different cells, tissues or organs essential for human life. The approach highlights the contribution that functional biochemistry makes to health and, when it is disturbed, to ill health and disease. It attempts to link biochemistry, medical education and clinical practice. Structural biochemistry and molecular biology are kept to a minimum in favour of a focus on the dynamic aspects of biochemistry and its immediate importance for health.