During the first meiotic cell division (meiosis I), homologous chromosomes pair, synapse, recombine, and segregate, using highly coordinated and tightly regulated mechanisms. The synaptonemal complex (SC), a proteinaceous tripartite structure, plays an important role both as a scaffold for the close juxtaposition of homologous chromosomes and in regulating the overall process of homologous recombination. Specifically, it mediates chromosome synapsis during the lengthy prophase of meiosis I. The SC consists of two parallel lateral elements, one central element, and numerous transverse filaments. Recent genetic studies in mice have provided novel insights into the mechanisms by which the SC regulates meiosis and into the etiology of diseases such as aneuploidy. Even though the tripartite ultrastructure and meiotic functions of the SC are similar in different species, the SC components are not well-conserved at the protein sequence level. This review will focus on the identification, characterization, and functions of the synaptonemal complex proteins in mammals.