A method and system for ranking documents of search results based on information richness and diversity of topics. A ranking system determines the information richness of each document within a search result. The ranking system groups documents of a search result based on their relatedness, meaning that they are directed to similar topics. The ranking system ranks the documents to ensure that the highest ranking documents may include at least one document covering each topic, that is, one document from each of the groups. The ranking system selects the document from each group that has the highest information richness of the documents within the group. When the documents are presented to a user in rank order, the user will likely find on the first page of the search result documents that cover a variety of topics, rather than just a single popular topic.