Eukaryotic cells are partitioned into functionally distinct organelles. Long considered as independent units in the cytosol, organelles are actually in constant and direct interaction with each other, mostly through the establishment of physical connections named membrane contact sites. Membrane contact sites constitute specific active regions involved in organelle dynamics, inter-organelle exchanges and communications. The endoplasmic reticulum (ER), which spreads throughout the cytosol, forms an extensive network that has many connections with the other organelles of the cell. Ample connections between the ER and endocytic organelles are observed in many cell types, highlighting their prominent physiological roles. Even though morphologically similar-a contact is a contact-, the identity of ER-Endosome contacts is defined by their specific molecular composition, which in turn determines the function of the contact. Here, we review the molecular mechanisms of ER-Endosome contact site formation and their associated cellular functions. This article is part of a Special Issue entitled Endoplasmic reticulum platforms for lipid dynamics edited by Shamshad Cockcroft and Christopher Stefan.