For at least several centuries, sargasso has inhabited the Atlantic Ocean, and there are historical records of these algae reaching the Mexican Veracruz State in the Gulf of Mexico. Blooming of sargasso in the southern tropical Atlantic is a current a global problem from Africa to the Greater Caribbean. Since 2015, exceptionally large quantities of sargasso have been arriving intermittently on the Mexican Caribbean coast, affecting coastal ecosystems and tourist beaches. Sargasso includes two holopelagic species, Sargassum natans and S. fluitans, with several varieties. There are no records of sexual reproduction in these species, and the algae are thought to spread exclusively by clonal reproduction by fragmentation. Although sargasso seaweeds have grown in the Sargasso Sea for centuries; they have not been well studied. This chapter deals with historical aspects of these algae, their taxonomic and morphological characteristics, distribution, ecology, and practical uses. Sargasso blooms in the central Atlantic started in 2011. In later years, the bloom developed to extend from West Africa, Brazil, and the Great Caribbean, including West-Indies, Mexico, and the Gulf of Mexico. The pelagic sargasso is a global phenomenon that must be understood by integrating natural history, modern biology, social and economic aspects.