The highly sequence-selective molecular recognition of proteins and peptides in Nature inspires and informs the development of synthetic receptors to mimic, measure, and modulate these processes. This chapter focuses on the cucurbit[n]urils, which have been particularly powerful in this regard. We describe the discovery and elaboration of the sequence-selective recognition of peptides by cucurbit[n]urils. In addition, we overview the development of this supramolecular chemistry into myriad applications and the extension to protein recognition. Finally, we compare the binding properties of synthetic receptors with those of natural N-recognins, proteases, and other sequence-selective protein receptors. The strong correlation between natural and synthetic receptors in their molecular basis for sequence recognition should serve to improve the design of next-generation compounds.