A system and method is disclosed for generating numerical index terms for numbers encountered in documents indexed by a search engine. The numerical index terms include information about the indexed number (e.g., fieldname, characteristic, sign) and each digit, or a subset of the digits, of the number (e.g., position, value). Also, disclosed is a system and method of processing number-range search queries having one or more number ranges and generating expressions (e.g., Boolean expression tree) of numerical index terms based on a boundary number associated with the number range. An expression is used to control the search of a document index so as to identify documents that contain numbers that satisfy the expression.