Far from terrestrial noise sources, and as an interferometer with extremely long arms, LISA is tailor-made to study low frequency gravitational waves, which oscillate no more than once in ten seconds. As such, LISA is ideal to study supermassive black holes, which can be found in the core regions of most galaxies (such as the galaxy NGC1300 shown here): Both the signals of smaller black holes spiraling into a supermassive hole and the gravitational waves produced in the merger of supermassive holes should be accessible to LISA. Also, LISA is set to study gravitational waves produced in the very early universe, less than a trillionth of a second after the big bang. Finally, there is a less exotic class of targets: the gravitational waves produced by ordinary double stars.