Content -- Employers want to know you feel you can fit in at the company quickly. That means not only deliverables in the job description, but also your fit with the company culture. You will likely have to do some homework to answer this one. You need to understand the reasons why others enjoy working there. Is it a great place to advance your skills, have great challenges to add to your resume, or will it allow you to grow as a professional?
Any candidate can read and regurgitate the company’s “About” page. So, when interviewers ask this, they aren't necessarily trying to gauge whether you understand the mission—they want to know whether you care about it. Start with one line that shows you understand the company's goals, using a couple key words and phrases from the website, but then go on to make it personal. Say, “I’m personally drawn to this mission because…” or “I really believe in this approach because…” and share a personal example or two.