Cysteine-rich peptides are highly abundant in nature, and provide a fascinating insight into protein folding, structure, chemical modification and function. The largest number and diversity of cysteine-rich peptides are produced by organisms at the interface between predator and prey, and host and pathogen (or symbiont). The small peptides produced by these organisms are characterized by hypervariable sequences interspersed with conserved cysteines involved in disulfide bond formation, and include some of the fastest evolving genes in nature. The diversity of structural scaffolds found for cysteine-rich peptides suggests that specialized adaptations have evolved to ensure their efficient folding and secretion in their producer organisms. This chapter uses conopeptides, neurotoxic peptides found in the venoms of predatory marine cone snails, as model systems to discuss some of these adaptations discovered in organisms that provide a rich source of cysteine-rich peptides with diverse structural scaffolds.