Triacylglycerols (TAGs) constitute a highly efficient form of energy storage. In seeds of angiosperms, they can act as a reserve of carbon and energy allowing to fuel post-germinative seedling growth until photosynthesis becomes effective. They also constitute the economic value of seeds in many crops. In the past years, extensive tools allowing the molecular dissection of plant metabolism have been developed together with analytical and cytological procedures adapted for seed material. These tools have allowed gaining a comprehensive overview of the metabolic pathways leading to TAG synthesis. They have also unravelled factors limiting oil production such as metabolic bottlenecks and light or oxygen availability in seed tissues. Beyond these physiological aspects, accumulation of TAGs is developmentally regulated in seeds. The oil biosynthetic process is initiated at the onset of the maturation phase, once embryo morphogenesis is achieved. A wealth of recent studies has shed new lights on the intricate regulatory network controlling the seed maturation phase, including reserve deposition. This network involves a set of regulated transcription factors that crosstalk with physiological signaling. The knowledge thus acquired paves the way for the genetic engineering of oilseed crops dedicated to food applications or green chemistry.