The fossil record shows that life has experienced five major mass extinctions. A sixth catastrophe may be underway. Past mass extinctions were geologically short-lived intense crises that affected animals and plants in all environments. They removed the dominant and abundant species, leaving ecological voids to be filled by groups that were often rare or insignificant beforehand. Uniquely, the big five also saw the collapse of the base of the food chain in the oceans. The current extinction crisis does not yet have any of these attributes, but there are concerns over rising species extinction rates. ‘Extinction today and efforts to stop it’ compares current extinction rates with those of the past, and considers different terrestrial and marine conservation approaches.