What are the recommended textbooks?

No textbook that is introduced here should be read primarily for the purpose of preparing for the USNCO exam ^[with the exception of organic chemistry], but just to dive deeper into different fields of chemistry. For more information, please read our introductory guide.

Inorganic Chemistry

Miessler's Inorganic Chemistry: The textbook is compact, concise, and overall provides a decent introduction to the field, although some of its explanations are rather confusing and difficult to understand.
Housecroft's Inorganic Chemistry: The textbook is long, detailed, and very dense. Most of its explanations are simple, but it contains a lot of trivial knowledge that isn't required for the Chemistry Olympiads exam.

Organic Chemistry

Klein's Organic Chemistry: well explained, simple, introductory, focused on mechanisms. This is the only organic chemistry textbook that is truly required for Chemistry Olympiads, but might not be sufficient for competitions harder or equivalent to IChO.
Clayden's Organic Chemistry: Well explained, detailed, also focused on mechanisms, but also very well organized. This is one of the best books in the field of Organic Chemistry, but very overkill for most Chemistry Olympiads.
Wade's Organic Chemistry: A typical college organic textbook, that you should avoid at all costs.
Advanced Organic Chemistry Textbooks: Carey and Grossman are popular, but these are often for graduates and you wouldn't be reading these textbooks for Chemistry Olympiads.

Physical Chemistry

Atkins' Elements of Physical Chemistry: well explained, decent introduction to physical chemistry, and doesn't go into too advanced mathematics. If you are truly interested in this field, you should check out this book. It is the middle ground between Atkins' Chemical Principles and Atkins' Physical Chemistry.
Atkins' Physical Chemistry: A typical Physical Chemistry textbook that is used by many colleges. Although it isn't very special. Not recommended. McQuarrie's Physical Chemistry: A Molecular Approach: This is infamously known to be one of the best physical chemistry textbooks to be ever written.

Analytical Chemistry

Harris' Quantiative Chemical Analysis: For an analytical chemistry textbook, it's a very decent book. It's great practice for advanced calculations (with good practice problems) and is a decent read.

Biochemistry

Lehninger Principles of Biochemistry: As the Russian IChO gold medalist famously says, "I didn’t buy a book to prepare for the Olympiads except for Albert L. Lehninger’s works. There are plenty of resources online"¹, this book is legendary and no other biochemistry textbook can compare. Should you read it for USNCO? Of course not