Receptor-mediated endocytosis is a cellular process that allows cells to take in specific molecules from their environment. This process begins when a molecule, such as a hormone or nutrient, binds to a specific receptor on the cell's surface. The binding triggers the cell membrane to invaginate, or fold inward, forming a small pocket that eventually pinches off to create a vesicle containing the bound molecules. This method is highly selective, meaning that only molecules that fit the specific receptors are taken in, ensuring that the cell receives the necessary substances while avoiding unwanted materials. Receptor-mediated endocytosis is crucial for various cellular functions, including the uptake of cholesterol, iron, and certain viruses.