<p>Historic and ongoing efforts in ecology and environmental science have highlighted the pressing need to monitor the health, sustainability and productivity of global and local ecosystems. Interest in these areas reflects a need both to determine the suitability of environments to support human activity (settlement, agriculture and industry) and to evaluate the impacts of such anthropogenic action. Of interest are chemical, biological and physical factors that reduce ecosystem viability owing to human intervention. Evaluating these factors and their impact on global health, ecological stability and resource availability demands improvements to existing environmental sensing technologies. Current methods to quantify chemical pollutants, biological factors and deleterious physical conditions affecting target ecosystems suffer from lack of automation and narrow spatiotemporal range. Recent advances in materials science, chemistry, electronics and robotics offer solutions to this problem. A vision emerges for fully autonomous, networked and ecoresorbable sensing systems that can be deployed over large aerial, terrestrial and aquatic environments. This Review describes ongoing efforts in these areas, focusing on materials advances supporting the accurate quantification of environmental factors with apparatus that accommodates full or partial device resorption. Discussion begins with an overview of hazards affecting global ecosystems, followed by a description of existing detection methods to quantify their severity. We proceed with an exploration of existing and developing technologies affecting sensor dispersion, motility, communication and power. Finally, we describe exciting recent efforts in the development of environmentally degradable materials that could prove beneficial in the realization of massively distributed (millions of individual sensors) transient sensor networks.</p>