Cell organelles are subcellular structures characterized by specific functionalities. They often consist of membrane-delineated microcompartments with a unique set of enzymes. Here we report the design of synthetic organelles based on nanometer-sized polymer vesicles, show their introduction into cells in a target-specific fashion, document their intact biochemical functionality in the cellular environment, and study their intracellular trafficking. This novel paradigm of introducing polymer-based artificial organelles to specific target cells for expansion of their biochemical capabilities appears suited for biomedical applications such as enzyme replacement in genetic diseases or, more generically, to add a desired biochemical function to a cell.