My initial communication with the company was through an email asking for a good time for a phone interview. It was concise and somewhat casual. The phone interview was also casual and did not cover much more than my background and interest. A few days later, I was offered the opportunity to visit the headquarters for a "meet and greet". It was unclear what the itinerary was. It was surprising to see a variety of dress from different interview candidates - some were formal and others were fairly casual. The staff we met were extremely casual and friendly, but professional. It was basically a free-for-all networking event. Food and drinks were provided as staff and candidates mingled. At the end of networking, we were given a tour of the headquarters. It was modern and fun. It was difficult to get a sense for what kind of personality they were looking for. As a start-up, the company appeared to be trying to stay casual and fun. I'm not certain dressing in business formal will work to an interviewer's advantage.