Widely accepted views among technical personnel and particularly developmnent programme administrators are that the explanation of widespread range of degradation in pastoral areas lies in the problem of common property (whereby private benefits from putting additional livestock on the range exceed social benefits), and that, more generally, pastoralists have an "irrational" propensity to accumulate stock. The policy conclusions drawn int his paper relate to the appropriate level of water investment and veterinary programmes. The paper exposes major deficiencies of logic in the standard arguments and explores the rationale of pastoral economic behaviour in a mroe systematic way.