Mesoderm is one of the three germ layers in the early developing embryo, the other two layers being the ectoderm and the endoderm. The mesoderm gives rise to tissues including connective tissue, muscles and the circulatory system. The mesoderm is also believed to be responsible for the formation of the central nervous system.

In a developing vertebrate embryo, the mesoderm differentiates into the areas, the paraxial mesoderm, the intermediate mesoderm and the lateral plate mesoderm.

The paraxial plate mesoderm lies along the central axis, and gives rise to the notochord and neural tube. The intermediate mesoderm develops into the urogenital system.

The lateral plate mesoderm is found at the periphery of the embryo. This in turn splits into two layers, the somatic layer/mesoderm and the splanchnic layer/mesoderm. Enclosed between the two is a space called coelom. The somatic layer forms the future body wall, and the splanchnic layer forms the future gut wall.

Because the Mesoderm can form different ways in relation to the developing embryo's Ectoderm, this is used as a method of categorizing Animals. They are catagorized as: Acoelomates, Pseudocoelomates, and Coelomates respectively.

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