1. A method for advertisement placement, comprising: obtaining one or more advertisement query keywords; determining, using one or more computer processors, in a multi-level advertisement information store, a selection of advertisement information for placement; and presenting the selection of advertisement information to be placed at a client; wherein: the multi-level advertisement information store comprises advertisement information organized into a plurality of first-level categories, and each first-level category is associated with a respective plurality of subordinate levels of categories; and determining, in the multi-level advertisement information store, the selection of advertisement information for placement includes: determining a first-level category based at least in part on the one or more advertisement query keywords; locating in each of the plurality of subordinate levels of categories associated with the first-level category, candidate advertisement information that corresponds to the one or more advertisement query keywords; and making the selection of advertisement information for placement based on the candidate advertisement information.