This chapter discusses the venomous peptides found in sea anemone. Sea anemones, in common with other members of the phylum Cnidaria (Coelenterata), possess numerous tentacles containing specialized stinging cells or cnidocytes. These stinging cells are equipped with organelles known as nematocysts that contain small threads which are forcefully everted when stimulated mechanically or chemically. Anemones use this venom apparatus in the capture of prey (crustaceans, small fish), as well as for defense against predators and in intra-specific aggression. The two most thoroughly characterized classes of peptides and polypeptides from sea anemones are the 5 kDa toxins that act by binding to voltage-gated sodium channels and the 20 kDa cytolysins, called actinoporins. Sodium Channel Toxins consists of at least three classes of peptides, two made up of molecules containing around 45-50 amino acid residues and one of shorter peptides containing 27-32 residues. These toxins bind to site 3 on voltage-gated sodium channels (VGSC), one of at least seven toxin binding sites identified on vertebrate and insect channels. Further, a unique family of potassium channel blockers has been identified in anemones. The first representative to be isolated and characterized thoroughly in potassium channel toxins was ShK, from Stichodactyla helianthus. The actinoporins display permeabilizing activity in model lipid and cell membranes and function by forming pores in cell membranes.