Some of the things binaries do...

Stellar astrophysics has undergone a transformation over the last two decades where it has become apparent that interactions of binary stars must be considered in all stellar populations. In this talk I will outline some of the evidence for the importance of binary stars for resolved and unresolved stellar populations, high-redshift galaxies, supernovae and gravitational wave transients. I will then end discussing where there are still gaps in our knowledge of binary stars and the steps we can take to obtain a complete understanding of binary stars.