Myoglobin (Mb) and Hemoglobin (Hb), the respiratory pigments of mammals and some molluscs, annelids and arthropods, belong to an ancient super-family of heme associated globin proteins. Members of this family share common structural and spectral features. They also share some general functional characteristics such as the ability to bind ligands, e.g. O₂, CO and NO, at the iron atom and to undergo redox changes. These properties are used in vivo to perform a wide range of biochemical and physiological roles. While it is acknowledged that the major role of Hb is to bind oxygen reversibly and deliver this to the tissues, this is not the sole function of the protein. In addition, the often-stated role of Mb as an oxygen storage protein is possibly a misconception. Both Hb and Mb may, for example, express enzymic activities that are important to their function e.g. NO oxidase activity or peroxidatic activities that may be partially responsible for pathophysiology following haemorrhage. The biochemical and biophysical evidence for these functions will be described and the discussion extended to include proteins that have been discovered comparatively recently and that are expressed at low levels within the cell, e.g. the neuroglobins and cytoglobins. These proteins are wide spread throughout the animal and plant kingdoms and may have specialist roles in oxygen delivery to particular sites within the cell but may also perform roles associated with O₂ sensing and signalling and in the organism’s response to stress e.g. by providing protection from reactive oxygen species. Similarly, hemoglobins are widespread in plants and bacteria and may serve similar protective functions. The talk will present the essential features shared by these proteins and discuss how these are tuned in different organisms to accomplish an extensive range of physiological tasks.