The IRS is a Bureau of the Department of the Treasury. This means that it is ultimately answerable to the Secretary of the Treasury:
The Internal Revenue Service publishes hundreds of guides to specific tax issues, along with forms, in print and electronic form. The print copies are available at IRS district offices, by mail request, and as downloadable files in PDF format from the IRS web site. These are generally accessed by name and/or publication number.
The Internal Revenue Manual compiles the operating procedures of the IRS.
Various IRS Forms & Publications are available at: IRS Forms, Instructions & Publications