There are a number of ways to assess the culture. Yes, the CEO and his/her style leads the culture but keep in mind the CEO is going to put together a leadership team that can executive on his/her vision. Look at the leadership team and how they operate. They are closest to the working staff and set the tone. I would also go out to their website, read their recruiting posts…how do they define themselves to the public when looking to hire employees. I think another way to assess the culture is understanding what is important….profitable growth, or just growth? In the early stages of a start-up, it is most likely just growth, so how fast are they moving to accomplish that? In the early stages of a start up, most people are sprinters…they need to move fast to get to market. They hire sprinters that can wear multiple hats. The next stage might be rock climbers…a lot of tough work ahead of them and they need to be more careful in execution and more specialized in their role. In many situations the culture begins to shift as the company grows….but there will always be a mission and purpose that doesn’t change.