After a patient encounter, the physician uses two coding systems to bill for the service rendered to the patient. The Current Procedural Terminology (CPT) code is used to describe the encounter or procedure. The International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) code is used to describe the diagnosis(es) of the patient. On October 1, 2015, ICD-9-CM coding will end, and all physicians will be required to use a new diagnostic coding system, the International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM). This article describes the new diagnostic coding system and how it differs from the old system. There are resources and costs involved for physicians and physician practices to prepare properly for ICD-10-CM. Similar to other important events, the more thorough the preparation, the more likely a positive outcome will occur. Resource use is very important in preparation for the transition from ICD-9-CM to ICD-10-CM. Greater familiarity with ICD-10-CM plus a thorough, effective preparation will lead to reduced costs and a smooth transition. Coding descriptor changes and additional codes occur in ICD-10-CM for chronic bronchitis and emphysema, asthma, and respiratory failure. These changes will affect the coding of these diseases and disorders by physicians. Because the number of codes will increase more than fivefold, the complexity of documentation to support ICD-10-CM will increase substantially. The documentation in the patient’s chart to support the ICD-10-CM codes used will need to be enhanced. The requirement for accurate and comprehensive documentation cannot be emphasized enough. All of the coding and documentation changes will be a challenge to pulmonary, critical care, and sleep physicians. They must be prepared fully when ICD-10-CM coding begins and ICD-9-CM coding stops abruptly on October 1, 2015.