This chapter presented an overview of the role of proteins as biological effectors. From a simplistic point of view, based solely on comparison of the structural diversity of immunoglobulins, blood coagulation proteins, gonadotropins, growth factors, and antiproteins, it could be concluded that the functional mechanisms of these protein families bear little or no relationship. Despite this enormous divergency in structure-function relationship, there are in fact elements of commonality in their effector roles arising as a direct consequence of the ability of these classes of protein effectors to act as exquisite examples of the processes of biorecognition. All these case histories, and the numerous other familial case studies of protein effectors which could have been employed to illustrate the different functional roles of proteins, owe their biological properties to their primordial protein antecedents which have traversed the harsh wilderness of evolution in biorecognition phenomena and survived to elicit specific effector roles. Dictated by underlying physicochemical constraints, deceived at times by the lulling tones of the siren entropy, and constantly vulnerable to the vagaries of other more pervasive forms of biological networking and information transfer encoded in the genes of virus and invading microorganisms, protein biorecognition in higher life forms, and particularly in mammals, represents the finely tuned molecular avenues for the genome to transfer its information to the next generation. The examples summarized in this chapter illustrate the complex, and in disease states imperfect, functional potential of proteins to be manifested in the jigsaw of biorecognition and be realized in the network of nature's biological effectors. Proteins thus represent a diverse range of effector molecules whose properties are totally dependent on their conformational or topographic status. The three-dimensional structure defines active sites on the molecule through which intermolecular interaction and biorecognition phenomena can occur. The cipher for this surface topography is, of course, coded in the primary amino acid sequence. Much experimental work is being directed in these and other laboratories at elucidating the principles governing the folding of unique peptide sequences into three-dimensional structures. Further advances in the theoretical understanding of the thermodynamics of protein folding as observed by x-ray crystallography, nuclear magnetic resonance and other spectroscopic techniques will greatly aid this quest. In addition, more comprehensive computer-aided algorithms for structure simulation, improved models of protein conformational behavior, and greater insight into the molecular forces which control sequence nucleation will also be required.(ABSTRACT TRUNCATED AT 400 WORDS)