Fairly straightforward - only 1 interview round that I had to go through before getting hired. Like most nonprofits, they want to see whether you are passionate about their mission. Study their mission, their work and tell them how you can contribute to their mission. They want mission-driven people, not money though money would be nice. I am not sure whether they increased their pay scale, but be sure that you can live off with the pay you make. They are not the only org that's making a change in the world, so make sure you know what you getting in before you accept the offer.