Chapters/Basement

The Basement is the first floor in The Binding of Isaac, which takes the appearance of an unfinished basement, that possibly has brick walls. The final boss of the level is Little Ghost. The monsters "Indigenous" to the chapter are Flies.
==Rooms==
* 1: The room will always appear once in this floor
* 2: The room will always appear twice in this floor
* Possible: There is a chance for this room to appear, usually due to certain criteria being met
* *: This room can only appear due to a bug or special item
* -: The room cannot appear in this floor.
Rooms with the core game 	Rooms with the core game 	Rooms with the core game 	Rooms with the core game 	Rooms with the core game 	 	 	 	 	
Rooms 	Basement 1 	Basement 2 	Basement XL 	Note 	 	 	 	 	
Regular Rooms 	7 - 11 	13 - 14 	- 	The player must have Wrath of the Lamb installed for The Basement XL to appear. 	 	 	 	 	
Treasure Room 	1 	1 	2 	Both Treasure Rooms are locked in The Basement XL. 	 	 	 	 	
Shop 	1 	1 	1 	There is always one shop, even in XL floors. 	 	 	 	 	
Secret Room 	1 	1 	1 	 	 	 	 	 	
Boss Room 	1 	1 	2 	Boss Rooms are always linked in XL floors. 	Rest	1	1 	2 	This is where you fight Little Ghost.
Challenge Room 	- 	Possible 	Possible 	Will only be generated if Isaac has full health while entering the floor. Cannot appear in The Basement 1.	 	 	 	 	
Arcade 	- 	Possible 	- 	Only generated when Isaac has 5 Coins upon entering a new floor or part. 	 	 	 	 	
Devil Room 	* 	Possible 	Possible 	*Only reachable by The Joker card. 	 	 	 	 	
I AM ERROR 	Possible 	Possible 	Possible 	Only reachable by using the Telepills, which have a 6.66% chance to teleport Isaac to this room. 	 	 	 	 	
Rooms with Wrath of the Lamb	Rooms with Wrath of the Lamb	Rooms with Wrath of the Lamb	Rooms with Wrath of the Lamb	Rooms with Wrath of the Lamb 	 	 	 	 	
Rooms 	Basement 1 	Basement 2 	Basement XL 	Note 	 	 	 	 	
Super Secret Room 	1 	1 	1 	 	 	 	 	 	
Curse Room 	Possible 	Possible 	Possible 	 	 	 	 	 	
Sacrifice Room 	Possible 	Possible 	Possible 	 	 	 	 	 	
Angel Room 	* 	Possible 	Possible 	*Only reachable by The Joker card. 	 	 	 	 	
Library 	Possible 	Possible 	Possible 	5% base chance to spawn, 25% if Isaac is holding a book. 	 	 	 	 	
Slamerd 	* 	Possible 	Possible 	This room is unlocked with Night's Slamerd 	 	*	Possible	Possible	*Only reachable by playing as Isaac or Night.