The endoplasmic reticulum (ER) is a dynamic organelle with multiple functions, including protein synthesis, lipid metabolism, and calcium storage. The ER consists of distinct domains such as tubules, sheets, and the nuclear envelope, each performing specific roles. Proteins that contribute to the ER's architecture and dynamics have been identified, but many questions remain about how the ER changes shape in response to cellular cues, cell type, cell cycle state, and developmental stages. This review discusses the dynamics of the ER, the proteins involved in its structure, and how these dynamics are regulated. The ER is composed of a continuous membrane system, including the nuclear envelope and peripheral ER, which includes smooth tubules and rough sheets. The shape and distribution of these domains are regulated by various integral membrane proteins and interactions with other organelles and the cytoskeleton. Key proteins that promote ER tubule formation include reticulons, DP1/Yop1/REEP5/6, and REEP1-4, while atlastins mediate homotypic fusion events. Recent studies have identified new players in ER dynamics, such as Rab10 and Rab18, which are involved in ER assembly and fusion. The ER also interacts with microtubules, and changes in ER structure during mitosis and oocyte maturation are discussed. During mitosis, the ER undergoes dramatic shape changes, primarily forming sheets, and the distribution of ER shaping proteins is altered. In oocyte maturation, the ER reorganizes into clusters, which are associated with calcium signaling and fertilization. Understanding the regulation of ER dynamics is crucial for comprehending cellular processes and their disorders.The endoplasmic reticulum (ER) is a dynamic organelle with multiple functions, including protein synthesis, lipid metabolism, and calcium storage. The ER consists of distinct domains such as tubules, sheets, and the nuclear envelope, each performing specific roles. Proteins that contribute to the ER's architecture and dynamics have been identified, but many questions remain about how the ER changes shape in response to cellular cues, cell type, cell cycle state, and developmental stages. This review discusses the dynamics of the ER, the proteins involved in its structure, and how these dynamics are regulated. The ER is composed of a continuous membrane system, including the nuclear envelope and peripheral ER, which includes smooth tubules and rough sheets. The shape and distribution of these domains are regulated by various integral membrane proteins and interactions with other organelles and the cytoskeleton. Key proteins that promote ER tubule formation include reticulons, DP1/Yop1/REEP5/6, and REEP1-4, while atlastins mediate homotypic fusion events. Recent studies have identified new players in ER dynamics, such as Rab10 and Rab18, which are involved in ER assembly and fusion. The ER also interacts with microtubules, and changes in ER structure during mitosis and oocyte maturation are discussed. During mitosis, the ER undergoes dramatic shape changes, primarily forming sheets, and the distribution of ER shaping proteins is altered. In oocyte maturation, the ER reorganizes into clusters, which are associated with calcium signaling and fertilization. Understanding the regulation of ER dynamics is crucial for comprehending cellular processes and their disorders.