  We introduce {\em Green fields}, as commutative Green biset functors with no
non-trivial ideals. We state some of their properties and give examples of
known Green biset functors which are Green fields. Among the properties, we
prove some criterions ensuring that a Green field is semisimple. Finally, we
describe a type of Green field for which its category of modules is equivalent
to a category of vector spaces over a field.
