For much of the last decade the use of column-based approaches has been very much a niche activity. However, with eight vendors (that we are aware of) now active in the market, with approaching 1,500 customers (many of them Global 2000 companies) between them, we believe that it is time for columns to step out of the shadows to become a major force in the data warehouse and associated markets. Given that view, this paper will define what column-based relational databases do and how they do it, and where they have advantages (and disadvantages) compared to traditional approaches. This in turn will lead to a discussion of the sort of environments for which columns are best suited.