Model of a self-reinforcing stepwise LD formation. Continuous lipid arrival promotes the formation of emerging LDs in ∼5 min. Initially, newly synthesized neutral lipids can be integrated in the ER membrane. However, addition of new triglycerides to the globule will promote phase separation and the deposition of the globule between the two leaflets of the ER bilayer. These globules produce a transient curvature of the ER membrane or move two-dimensionally within the bilayer, fuse with other globules, and generate curvature of the ER. Proteins with amphipathic α helices, such as HPos or ACSL3, are then attracted to these regions. The stable interaction of these proteins nucleates unstable globules and marks the onset of LD biogenesis. The enrichment of ACSL3 locally generates the acyl-CoA required for LD growth and expansion but also numerous bioactive lipid intermediates. Emerging LDs expand and the lipid intermediates are recognized by Plin proteins. If lipid supply ends, these structures become stable and remain connected to the peripheral ER. If lipid supply persists, emerging LDs increase in size to become early and mature LDs. Early and mature LDs accumulate in the central ER and are metabolized during starvation.