This paper was presented to the Fifth Conference of the Institute of Psychotherapy and Counselling whose overall subject was Envy. I chose the subject of sibling rivalry because I have always found it a burning personal issue. Surprisingly not much has been written about it; so I hoped it would be interesting for a change to think about an aspect of envy that is a universal experience and yet different from the primary envy which Melanie Klein located in the motherbaby relationship and the state of part object relating. Rivalry and competition begin in the later developmental phase when the infant has achieved unit status, and when the two-person relationship has expanded into three- and multi-person relationships where the issues are loss, exclusion and intrusion. Then the experience of difference and otherness has to be mastered so that socialisation can take place.