Hi Sarah: This is a great question - honestly, I don't think you have to go into details about the reasons why you were fired. Only reveal what's comfortable for you to reveal. You could even give a straightforward answer like, "My previous company and I didn't fit in terms of culture, so I'm looking to join a team like yours that has everything I'm looking for in a job" It's simple, straight-to-the-point, and doesn't require you to say the word "fired"!