In this contribution relationship-oriented assessment methods and preventive measures during infancy and childhood are founded in an ecological and differential understanding of development in context. Using selected developmental milestones it is demonstrated that relationships as a social context play an important role particularly during early infancy. Criteria for describing well functioning and maladaptive relationships can be derived from theoretical presumptions, empirical longitudinal studies and health related clinical judgements. These criteria may serve as guidelines for interventions, especially in cases of children with a clinical diagnosis of child neglect. Possible procedures to assess the quality of relationships are discussed using methods from contributions in this issue of the journal as examples. Diagnostic and preventive procedures are seen as mutually interacting within continuous feedback loops, where assessment procedures serve to both give evidence for the efficacy of interventions and for specifying further preventive methods.