In response to a user's submission of a set of query terms through an Internet search engine's user interface, the Internet search engine automatically ranks multiple verticals based on the estimated probabilities that those verticals will contain relevant content. After the verticals have been ranked, a set of the highest-ranked verticals is selected. Search results from each of the verticals in the selected set are presented to the user. Thus, the user may obtain a sample from verticals that are the most likely to contain relevant content. The search engine may rank a set of verticals based on historical search result selection data for similar sets of query terms. The historical search result selection data for a set of query terms indicates, for each vertical, the number of times that any user selected a search result from that vertical after conducting a search based on that set of query terms.