Object relations are central to contemporary structural theory. This paper first reviews the various ways in which the key concept object constancy has been used. To reconcile the apparent contradictions in definitions, the concept is viewed along a developmental continuum in which each step is defined by its functions. It is proposed that at its most mature stage, a capacity for affective self-regulation is achieved, a capacity that is central to characterological structure formation and optimal adaptation. Possible interferences with the achievement of mature object constancy are briefly explored.