*The Importance of Early Child Development*

Early child development and overall children's developmental trajectories have longterm implications for health, functioning, and earning potential as these children become adults. Importantly, failing to reach developmental potential contributes to the global cycles of poverty, inequality, and social exclusion. The recognition of the close connection between the development of the child and the development of families and communities has served as the basis for national and global initiatives in health and education in recent decades.

In 2015, for the first time, an international initiative—the 2030 Sustainable Development Goals (SDGs)—included an early childhood development goal. Specifically, SDG 4 is to ensure lifelong learning, early stimulation, increased length of schooling, school performance, and adult income. In addition, early childhood development is intricately linked to other SDG goals, poverty reduction, health and nutrition, equality for girls and women, and ending violence. Nevertheless, the risks for delay, disability and unmet potential in the early development of young children are still pervasive, particularly in low- and middle-income countries.

This editorial letter introduces the main contribution of this Special Issue and invites the readers to explore and share its content to benefit a wider audience. The Special Issue is dedicated to Early Child Development: from measurement to optimal functioning and evidence-based policy, it includes 15 open access papers addressing key topics of global interest and application.
