Methods and systems for indexing patent related prior art citations are disclosed. Electronic documents can be obtained from one or more patent information systems. An OCR process can be performed on some of the electronic documents. Citations within the documents can be identified and compared to a trusted records list. The citations can be associated with one or more predetermined categories. For example, citations can be categorized into groups such as when a reference is cited (e.g., with original filing, pre and post allowance), who provided the reference (e.g., cited by the applicant, or the examiner), and how the reference is characterized (e.g., statutory basis, combination of references). The citations and corresponding categories can be output to a user or made available for subsequent processing.