A system may include one or more databases to store comments relating to documents, the comments originating from first and second sources, where the comments from the first source include comments received from users via commenting functionality associated with browsers installed on client devices, and the comments from the second source include comments received from users independent of the commenting functionality associated with the browsers installed on the client devices. The system may also include one or more server devices to receive a request for comments relating to a particular document, search at least one of the one or more databases to identify comments relating to the particular document, and provide the identified comments for presentation in connection with the particular document.