Hydrogen has gained much attention due to its excellent potential in reducing CO2 emissions from the ironmaking section. Currently, three types of ironmaking processes are considered in Korea: (1)direct injection of hydrogen with hot air in the blast furnace(H2-BF), (2)utilization of hydrogen-rich gas in the reduction of iron ore in fluidized bed reactors (FINEX, or Fluidizing bed reactor with COG), and (3)utilization of green hydrogen in the reduction of iron ore in fluidized bed reactors (HyREX). In each process, scientific questions have been raised due to the modification of the reducing agent from carbon to hydrogen. In the conventional blast furnace operation, control of melt flow in the coke bed became an essential issue because the successive reduction of iron oxide may result in re-solidification of the first melt. In the fluidizing bed reactors, iron whisker formation and sticking would be problematic. When green hydrogen is used in the fluidizing bed reactors, the control of the gas flow rate and the supply of heat energy needs to be solved. In this presentation, scientific questions in the hydrogen-based ironmaking processes are introduced, and several key features to be answered are introduced.