The cultural-historical concepts: relational expertise, common knowledge and relational agency are introduced as central to the work of practitioners who offer a caring (care-full) relational approach to supporting the learning and development of others. Drawing on examples from the field, we examine how the concepts can explain interprofessional collaborations and the prevention of social exclusion, which may frequently include involving parents or carers in focusing on a difficult situation for a child. We consequently discuss and illustrate the concepts in professionals’ work with parents or carers, which aims at mutual support for a child’s social situation of development during transitions. We demonstrate how three concepts can explain how practitioners negotiate their way up a system to find additional support for a child who is in a situation of concern. Our final example is their use in an instrument that assesses the collaborative maturity of teams or networks. The use of the three relational concepts in pedagogy is detailed in Chapter 7.