Title: GW150914 and the next challenges in gravitational-wave observations Joint event with the "GR@100++" PCTS workshop. Note special time! For Gravity Group members who attend the seminar talk, there is a free lunch with the workshop participants, starting at Noon. The talk is open for everybody. If you’d like to attend the entire workshop, please register under http://pcts.princeton.edu/pcts/GR100-2016/GR100.html