Migratory marine species cross the oceans and entire continents throughout their life cycle. During their journeys, they pass through dozens of countries and cover large areas of the high seas, extensive spaces over which there is no national jurisdiction. As part of these travels, species are often negatively affected by human activities. This complex spatial and temporal interconnection created by migratory species, as well as their constant interaction with human beings, represents a huge challenge to ensure appropriate conservation of their populations. This demands national and coordinated work among countries. Multilateral Environmental Agreements are the main international and regional instruments to take care of these species, including migratory species. In the case of Eastern Pacific countries like Chile, Mexico and Peru, who share the same populations of migratory marine species, these agreements are critical to ensure marine fauna conservation. Risks for these species are not limited to the high seas. Limited information on them, as well as weak governance, common in these three countries, paves the way for illegal fishing, pollution and loss and deterioration of critical habitat, among other negative impacts. Although there have been important advances at the international level and through local policies, challenges remain in terms of implementing effective and efficient conservation measures. Some recent initiatives in other countries provide opportunities to guarantee the life cycle of migratory species.