  We consider item allocation to individual agents who have additive
valuations, in settings in which there are protected groups, and the allocation
needs to give each protected group its "fair" share of the total welfare.
Informally, within each protected group we consider the total welfare that the
allocation gives the members of the group, and compare it to the maximum
possible welfare that an allocation can give to the group members. An
allocation is fair towards the group if the ratio between these two values is
no worse then the relative size of the group. For divisible items, our formal
definition of fairness is based on the proportional share, whereas for
indivisible items, it is based on the anyprice share.
  We present examples in which there are no fair allocations, and even not
allocations that approximate the fairness requirement within a constant
multiplicative factor. We then attempt to identify sufficient conditions for
fair or approximately fair allocations to exist. For example, for indivisible
items, when agents have identical valuations and the family of protected groups
is laminar, we show that if the items are chores, then an allocation that
satisfies every fairness requirement within a multiplicative factor no worse
than two exists and can be found efficiently, whereas if the items are goods,
no constant approximation can be guaranteed.
