This review explores the role of individual opioid receptor types and signal transduction pathways on cell growth and differentiation. The findings reviewed herein provide suggestive evidence that while no single opioid receptor or peptide type exclusively regulates growth, depending on the cell type, the activation of all three (mu, delta, or kappa) opioid receptor types can affect maturation in a cell type-dependent manner. Specific developmental responses are determined primarily by how a particular opioid receptor type is coupled to intracellular signaling effectors. Moreover, the coupling of opioid receptors appears to be developmentally regulated, and these protein-protein interactions change during ontogeny. The diversity of opioid receptor types and intracellular effectors may be a mechanism by which individual cells discriminate among different opioid signals, and may permit diverse opioid signals to be translated into a unique developmental logic in distinct neuronal and glial subpopulations.