Many issues and factors conspire to make New Zealand’s farm managers extremely susceptible to the notion that the productivity of their farm operation will be improved by mineral supplements. What is the basis for this assertion? It is impossible in a short review such as this to deal with every potential mineral problem for every situation, so this paper considers four issues currently under debate: • The need to always meet (mineral requirement). • Some difficulties of diagnosis. • Strategic supplements to stimulate immunity. • Supplements to modify acid-base balance and rumen function.