Integrins comprise a family of 24 heterodimeric transmembrane receptors that mediate cell attachment to the extracellular matrix and are critical for cell signaling. There are four classes of integrins: collagen-binding, Arg-Gly-Asp (RGD)-binding, laminin-binding, and leukocyte integrins. Owing to their involvement in modulating various critical cellular processes including proliferation, migration, differentiation, and survival, integrins have been investigated as therapeutic targets. Important progress has been made in the structural elucidation of integrins in recent years. Here we examine the protein-ligand interactions of integrin complexes and the related structure-based drug design of integrin inhibitors. Published integrin structures in the Protein Data Bank (PDB) are examined to gain insights into integrin-ligand interactions as well as the conformational dynamics of integrins.