This paper, which is in two parts, presents the results and analysis of droplet impaction on a hot stainless steel surface. Part I of this study reports the results of analysis of high-speed visualizations of droplet impaction phenomena on a hot stainless steel surface, including the characteristics of reatomized droplets that are produced at high impact Weber numbers. The investigation extends to ranges of smaller droplets and higher velocities compared with published research. Part II will then provide the results and analysis of the droplet impaction heat transfer on a hot surface. The 3. 0 mm diameter flat stainless steel surface was heated to temperatures of 140 degrees C < T-w < 400 degrees C, and water sprays were produced from a droplet generation system based on an 80 mm diameter rotary cup. Droplet sizes in the range 20 mu m < D < 160 mu m were used, impacting with velocities of 5 ms(-1) < U < 18 ms(-1). Previous research relevant to the topic is reviewed. Physical models for different forms of droplet breakup in different regimes are developed from the new experiments and compared with existing models. Data are presented for the droplet spreading characteristics, as well as reatomized droplet characteristics, under relatively high impact Weber number conditions (i.e., 100 < We < 750), and for different boiling regimes. These data are correlated well using equations that can be justified by physical arguments.