The design of the Environmental Control System (ECS) of the COLUMBUS Attached Pressurized Module (APM) has lately undergone a series of major modifications. These were on one side due to the increased technical maturity of the program and on the other side due to the agreed common understanding amongst the three partners (NASA/ESA/NASDA) that some functions need to be considered at overall Space Station level and therefore their relevant implementation shall have an high level of commonality.A typical example was the introduction of a set of fire detection and suppression requirements which, being jointly applicable to the US, European and Japanese modules, led to significant modification of the APM internal architecture.The implementation of a similar design for the fire detection and suppression function ensures a unified approach for the safety management of the Space Station under emergency conditions related to these particular hazards.The evolution experienced in the Thermal Control System (TCS) part of the ECS was driven by design maturity and the need of resources management. The water loop architecture has grown from a single loop configuration to a double loop configuration. By this the availability of the thermal resources to the Space Station and therefore to each partner are optimized.The purpose of the paper is to present the status of the COLUMBUS APM ECS design after the first major program milestone, i.e. the System Requirement Review (SRR), to highlight those areas of the ECS design where fundamental changes have been introduced and to identify the rationale/main drivers for them.