How our cells achieve inner communication between their organelles is one of the fundamental questions in biology. The endoplasmic reticulum (ER) and the nucleus are the two largest compartments within our cells. The ER is the site where many proteins and fat molecules are built. The nucleus contains most of our genetic material and is separated from the rest of the cell by a boundary called the nuclear membrane, which is continuous with the ER membrane. When a cell grows, the nucleus has to grow and new proteins and fat molecules need to be supplied from the ER to the nucleus. The connection between the ER and the nucleus is hereby essential. However, it has been unclear how the ER is connected to the nucleus, how shape and number of the connections change to support nuclear growth, and which molecules regulate the connection and its function in inner cell communication. This gap in our knowledge is due to the technical challenge of visualising these connections, which requires high-resolution microscopy that can spatially distinguish the connections from the rest of the ER/nuclear membranes. Our lab is investigating the molecular mechanism that governs the structure and function of the ER-nucleus connection and how the connectivity impacts on ER-to-nucleus transport by combining live imaging and 3D electron microscopy with molecular perturbations and mathematical modelling.