Laser Interferometer Space Antenna (LISA) was adopted by ESA on January the 25th, manifesting the feasibility of detecting gravitational waves (GW) in the mHz frequency band. This talk is meant to describe the mission, the benefits and difficulties of going to space to detect GW as well as the challenge that the data analysis bears. Despite the complexity we expect to be able to test general relativity in the strong field regime. The efforts towards that goal are also presented here.