The ATHENA (Advanced Telescope for High ENergy Astrophysics) mission is steadily progressing both in terms of system studies and technology developments. The mission is currently in Phase B1 and is maturing towards a successful mission adoption. This paper describes the mission status including the main accomplishments achieved during this phase in terms of convergence of system and technological aspects. An overview of the different system studies is given including the latest programmatic assumptions, emphasizing on the Mirror Assembly demonstration and the critical interfaces between the mirror and the different facilities that are being developed in tandem to the mission. The reference telescope design is also described based on the Silicon Pore Optics (SPO) technology. The main design choices are explained as well as the modelling performed to ensure that all technological and system level constraints are met from plate level all the way to the mirror assembly level. The resulting effective area performance and budgeting is briefly described and future improvements are identified.
