The invention features antibodies, e.g., chimeric and humanized antibodies, that recognize (i.e., bind) P-selectin. The P-selectin antibodies prevent P-selectin from binding to its cognate receptor. The P-selectin antibodies can be used to treat inflammatory and thrombotic conditions, e.g., sickle cell disease, pain crisis associated with sickle cell disease, deep vein thrombosis, asthma, rheumatoid arthritis, psoriasis, and ischemia reperfusion injury in a patient in need thereof.