A fundamental hallmark of eukaryotic cells is their compartmentalization into functionally distinct organelles, including those of the secretory and endocytic pathways. Transport of cargo between these compartments and to/from the cell surface is mediated by membrane-bound vesicles and tubules. Delivery of cargo is facilitated by SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor)-mediated membrane fusion of vesicles with their target compartments. Vesicles contain a variety of cargos, including lipids, membrane proteins, signaling molecules, biosynthetic and hydrolytic enzymes, and the trafficking machinery itself. Proper function of membrane trafficking is required for cellular growth, division, movement, and cell-cell communication. Defects in these processes have been implicated in a variety of human diseases, such as cancer, diabetes, neurodegenerative disorders, ciliopathies, and infections. The elucidation of the mechanisms of SNARE assembly and disassembly is key to understanding how membrane fusion is regulated throughout eukaryotes. Here, we introduce the SNARE proteins, their structures and functions in eukaryotic cells, and discuss recent breakthroughs in elucidating the regulation of SNARE assembly and disassembly through the use of high-resolution structural biology and biophysical techniques.