It's official! Joe Biden has selected Kamala Harris as his running mate, making her the first Black woman and first person of Indian descent to be nominated for national office by a major party. In the days and weeks ahead, the choice will undoubtedly come under scrutiny, from the left and the right. But in a year that saw a resurgence of the Black Lives Matter movement, the mood on social media was primarily congratulatory—from heartfelt personal celebrations to commendations of this historic moment. Below, some of the best reactions on Twitter.