The National Academies of Sciences, Engineering, and Medicine's Chemical Sciences Roundtable organized a series of four seminars in the autumn of 2016 to explore the current advances, opportunities, and challenges toward unveiling this "chemical dark matter" and its role in the regulation and function of different ecosystems. The first three focused on specific ecosystemsâ€"earth, marine, and humanâ€"and the last on all microbiome systems. This publication summarizes the presentations and discussions from the seminars.