This article is a summary of the Sol Sherry Lecture of the Council on Arteriosclerosis, Thrombosis, and Vascular Biology, which was presented at the Scientific Sessions of the American Heart Association in November 2004. It highlights work from our laboratory, focusing mainly on new aspects of P-selectin and CD40L (CD154) biology and on the interplay of platelets and leukocytes in thrombosis and inflammation.