Background The Special Issue articles describe six systems of parental interventions and developmental care several differences among each of the approaches. Nevertheless, on a deeper level there are profound similarities shared across the six systems. These similarities are at the heart of developmental care in general and parental interventions in particular.

Aim The aim of this paper is to highlight the commonalities of these systems of developmental processes and parental interventions.

Materials and Methods We discuss the concept of symbiosis as a theoretical framework for entering into a new understanding of mother-infant and family systems biology based on perspectives that share themes of interconnection and mutualism.

Results There are many rigorous, empirical studies of co-regulation, mutualism and interdependence in the human parent-offspring system that is moving us forward into this new territory. Perspectives that emphasize interconnection and interpenetration, reciprocity and mutualism, and integration over reduction are expanding to fill the spaces needed to answer today's questions.

Discussion Recent contributions of perspectives on neurocognitive development have buttressed the symbiosis view with constructs of prenatal origins, such as 'co-embodiment' and 'co-homeostasis', that illuminate maternal-fetal reciprocities seen to underlie initiation and maintenance of developmental trajectories essential to support fetuses born prematurely into a NICU environment.

Conclusion The six systems of parental intervention and developmental care presented in this Special Issue represent foundational approaches to developmental care for prematurely born infants. All these approaches recognize forms of reciprocity and mutualism on many levels, always including the infants as active parts of multiple regulatory systems.