This monograph is edited on the basis of the lecture contents of invited speakers and some oral presentations at the IUBMB Symposium on Protein Structure and Function. The main theme was the molecular and biochemical studies on the structure and function of proteins. It covers the most recent advances in research on animal and bacterial toxins, plant enzymes and proteins, structural motifs and functional aspects of enzymes, biophysical and chemical characterizations of snake toxins by NMR spectroscopy, and molecular approaches for studying the structure-function relationship of proteins and enzymes. Most of the papers are based on data obtained in the authors' laboratory over the past few years and were written in a concise manner as review articles. They will be valuable reference for researchers and graduate students in this field of study.