The Golgi Apparatus modifies, sorts, and packages proteins and other molecules for storage or secretion. It is composed of stacked flattened sacs called cisternae. Materials enter at the cis-Golgi and undergo processing as they move through the medial cisternae toward the trans-Golgi, where they are packaged into vesicles for transport within the cell or for secretion. The Golgi works closely with the endoplasmic reticulum to receive, process, and transport cellular cargo.