Integrin ${alpha}X{eta}2$ performs a significant role in leukocyte functions including phagocytosis and migration, and binds to a variety of ligands, including fibrinogen, iC3b, and ICAM-1. A particular domain of the ${alpha}$ subunit of the integrin - the ${alpha}X$ I-domain - is a ligand binding site, and the interaction of the ${alpha}X$ I-domain and ICAM-1 on the endothelium is an important step in leukocyte extravasation. In order to elucidate the structural aspects of this interaction, we defined the moieties of the ${alpha}X$ and ICAM-1 relevant to their interaction in this study. It was determined that the ICAM-1 binding sites of the ${alpha}X$ I-domain were located in the ${alpha}3{alpha}4$, ${eta}D{alpha}5$, and ${eta}F{alpha}7$ loops at the top surface of the I-domain. The residues $Q^{202}$, $K^{242}$, $K^{243}$, $E^{298}$ and $D^{299}$ on these loops were crucial for the recognition of ICAM-1. Among these residues, $K^{242}$ and $K^{243}$ on the ${eta}D{alpha}5$ loop were found to be the most salient, thereby suggesting an ionic interaction between these proteins. Domain 3 of ICAM-1 was identified as a primary binding site for the ${alpha}X$ I-domain. Two regions of domain 3 ($D^{229}$QRLNPTV and $E^{254}$DEGTQRL) perform critical functions in the binding of the ${alpha}X$ I-domain. Especially, the residue $E^{254}$DEG, is most important with regard to the ${alpha}X$ I-domain.