The Underground Notebook is a plastic ring binder in landscape format with six sections:
Each article in a section takes up the front and back of a single page. The "People" section provides some character creation tables, 40 deatiled NPCs and an NPC sheet. "Places" details eight regions, cities, and city blocks and includes a record sheet, too. "Organizations" describes 20 government and military organizations, religious groups and gangs. "Events" shows a timeline from 1998 to 2019 and has in-depth information about four major events. The "Technology" section is the shortest with only a few equipment tables. "Misc." has articles on various topics.
The Notebook was designed to hold more material that should be published with other Underground books in the appropriate notebook format.