Diagnosis CodesDiagnosis codes are known as ICD-9 codes, for International Classification of Diseases, 9th Version. You would get those codes out of an ICD-9 code book. This book is thick because it is so comprehensive. You want to get your information from the code book as opposed to getting it online because the book provides explanations of how to properly order the diagnoses for a patient's claim. Ordering diagnoses is very important in getting patient claims paid properly.
Procedure CodesProcedure codes are known by two names, depending on who you talk to. Generally, they're known as CPT-4 codes, which stand for Current Procedure Terminology, Version 4. Some people will call procedure codes HCPCS codes, which stands for Healthcare Common Procedure Coding System. These are level II codes which mainly describe supplies, products and pharmaceuticals, although there are a few procedure codes in this system as well..
There are also CPT-4 code books that are geared towards certain specialties such as radiology or endoscopic surgery. These are crucial for those departments to have because they give more detailed explanation of how and when to use these codes as opposed to most general CPT-4 codes, which will give some information but not in the same detail as the specialty-specific books.