Intracellular lipid droplets are utilized for lipid storage and metabolism in organisms as evolutionarily diverse as animals, fungi, plants, bacteria, and archaea. These lipid droplets demonstrate great diversity in biological functions and protein and lipid compositions, yet fundamentally share common molecular and ultrastructural characteristics. Lipid droplet research has been largely fragmented across the diversity of lipid droplet classes and sub-classes. However, we suggest that there is great potential benefit to the lipid community in better integrating the lipid droplet research fields. To facilitate such integration, we survey the protein and lipid compositions, functional roles, and mechanisms of biogenesis across the breadth of lipid droplets studied throughout the natural world. We depict the big picture of lipid droplet biology, emphasizing shared characteristics and unique differences seen between different classes. In presenting the known diversity of lipid droplets side-by-side it becomes necessary to offer for the first time a consistent system of categorization and nomenclature. We propose a division into three primary classes that reflect their sub-cellular location: i) cytoplasmic lipid droplets (CYTO-LDs), that are present in the eukaryotic cytoplasm, ii) prokaryotic lipid droplets (PRO-LDs), that exist in the prokaryotic cytoplasm, and iii) plastid lipid droplets (PL-LDs), that are found in plant plastids, organelles of photosynthetic eukaryotes. Within each class there is a remarkable array of sub-classes displaying various sizes, shapes and compositions. A more integrated lipid droplet research field will provide opportunities to better build on discoveries and accelerate the pace of research in ways that have not been possible.

细胞内脂质滴用于动物，真菌，植物，细菌和古细菌等进化上多样化的生物中的脂质存储和代谢。这些脂质小滴显示出生物学功能以及蛋白质和脂质组成方面的巨大差异，但从根本上具有共同的分子和超微结构特征。脂质小滴研究在脂质小滴种类和亚类的多样性上大体上是零碎的。但是，我们认为，更好地整合脂质滴研究领域对脂质群落具有巨大的潜在利益。为了促进这种整合，我们在整个自然世界研究的脂滴范围内，调查了蛋白质和脂质的组成，功能作用以及生物发生的机制。我们描绘了脂滴生物学的全貌，强调不同类别之间的共同特征和独特差异。在并列显示脂质液滴的已知多样性时，有必要首次提供一致的分类和术语系统。我们提议将其分为三个主要类别，以反映其亚细胞位置：i）真核细胞质中存在的胞质脂质滴（CYTO-LDs），ii）真核细胞质中存在的原核脂质滴（PRO-LDs） iii）质体脂质滴（PL-LDs），存在于植物质体，光合真核生物的细胞器中。在每个类别中，都有大量子类别，可显示各种大小，形状和成分。