  Since the 2017 Nobel Prize in Physics was awarded for the observation of
gravitational waves, it is fair to say that the epoch of gravitational wave
astronomy (GWs) has begun. However, a number of interesting sources of GWs can
only be observed from space. To demonstrate the feasibility of the Laser
Interferometer Space Antenna (LISA), a future gravitational wave observatory in
space, the LISA Pathfinder satellite was launched on December, 3rd 2015.
Measurements of the spurious forces accelerating an otherwise free-falling test
mass, and detailed investigations of the individual subsystems needed to
achieve the free-fall, have been conducted throughout the mission. This
overview article starts with the purpose and aim of the mission, explains
satellite hardware and mission operations and ends with a summary of selected
important results and an outlook towards LISA. From the LISA Pathfinder
experience, we can conclude that the proposed LISA mission is feasible.
