Industrial plant modularization represents one of the main drivers for competitiveness for clients and main contractors in the future decades. Casale is extensively using modularization for the green & blue ammonia and hydrogen plants. Benefit and drawback vs “stick-built” method will be analysed and discussed taking in consideration the specific aspects of our market sector. Modularization shall start at the very early stage of the project, together with process design activity. Typical workflow will be shown and explained. Casale experience on two projects: green ammonia with small modules and large modules is presented with figures and key factors.