There are three types of codes that you should be aware of: ICD-9, CPT, and HCPCS. They describe the diagnosis, physician services (examination & treatment plan, and/or procedures), and nonphysician services, respectively. The most basic aspect of this competency that coders need to learn is the rules of patient encounter coding. There are different levels assigned to the three main key components of E/M: history, examination, and medical decision making. All three components must meet or exceed requirements for a particular level in order to assign that level�s code to an initial encounter with the patient. During subsequent (also called established patient) encounters, only two of the three components should meet or exceed the level assigned to the entire encounter. Other components of E/M services that may impact on coding and billing include counseling, coordination of care, nature of the presenting problem and time spent face to face with the patient. Billing for various levels of these elements must be supported by adequate documentation according to published guidelines. The physician may choose to document a general multi-system examination or one of 11 single organ systems according to specific guidelines.