Gastrulation is a crucial phase in embryonic development that follows fertilization and cleavage, during which the single-layered blastula reorganizes into a multi-layered structure known as the gastrula. This process involves the movement and differentiation of cells, leading to the formation of the three primary germ layers: ectoderm, mesoderm, and endoderm. These layers give rise to various tissues and organs in the developing organism. Gastrulation is essential for establishing the body plan and spatial organization of the embryo.