The Endoplasmic Reticulum (ER) is a membraneous eucaryotic cell organelle that forms an interconnected network of tubules, vesicles, and cisternae within cells. The endoplasmic reticulum is divided into two categories, rough and smooth, depending on whether ribosomes exist or not on its surface, accordingly. The endoplasmic reticulum is responsible for protein translation, folding and transportation, certain post-translation modifications (such as glycosylation), and the production and storage of various macromolecules. For more info, see the related Wikipedia article: [1].