ABSTRACT: Populations of small pelagic fish (SPF), such as sardines, anchovies and herrings, support some of the largest marine fisheries globally and are critical for trophic transfer in large marine ecosystems and food security, particularly in low- to medium-income countries. Marked changes in population size, shifts in distribution on multiple time scales, and impacts on their populations from other pressures (e.g. overfishing, climate change) pose large challenges to sustainably manage these resources to avoid the serious socioeconomic and ecological impacts of population collapses. The ecology and management of SPF was discussed in an international symposium in Lisbon, Portugal, attracting participants from 38 countries and 6 continents. This Theme Section includes 18 research contributions examining SPF from 6 different ecological regions alongside 3 global analyses. These studies, including a wide range of topics from parasitology, behavior and trophodynamics to growth and spawning, provide important new knowledge that will improve science-based advice and tools needed for sustainable, ecosystem-based management of these resources. This symposium was an important milestone for a global working group and sowed the seeds for continued, globally coordinated research efforts on the role of SPF in complex socio-ecological systems.