The thermal behavior of a flow boiling system is represented by a flow boiling map to illustrate visually the relationships among various system parameters. An earlier flow boiling map by Collier (1981) does not include the effect of mass flux and is specific to water at low pressures. For other fluids, significant departures from the parametric trends displayed in Collier’s map have been reported in the literature (e.g., Kandlikar, 1988b). In the present paper, a new flow boiling map is developed to depict the relationships among the heat transfer coefficient, quality, heat flux, and mass flux for different fluids in the subcooled and the saturated flow boiling regions. The trends observed in the experimental data and correlations for water and refrigerants are used in deriving the present map. The particular areas where further investigation is needed to validate the trends are also indicated. In the subcooled boiling region, hTP /hlo is plotted against x with Bo as a parameter, while in the saturated boiling region, hTP /hlo is plotted against x with ρl /ρg and a modified boiling number Bo* as parameters. It is hoped that the map would prove to be helpful in explaining the role of different heat transfer mechanisms in flow boiling of different fluids.