A CNS is a masters degree prepared RN who specializes in a clinical specialty such as cardiology, geriatrics, oncology. The masters degree must be in a CNS program, that is to say in most states you cannot just go back to get a master's degree in nursing education or administration and then become a CNS. The master's program usually has 2-3 semesters of clinical course work in that specialty. My own master's degree is in critical care in a CNS program. I chose to structure all of my clinical course work in various phases of cardiac care such as cardiology, cardiac rehab, cardiovascular surgery and cardiac diagnostic testing. THen after you complete your degree you must sit for a national certification exam in your specialty. Mine is the CCRN but there are many choices to choose from. Then you apply to your board of nursing for licensure as a CNS and in my state you receive a certificate from the board of nursing stating that you are a licensed CNS. In many states you can apply for prescriptive authority and that is yet another part of your license if you choose to apply. All of your certification must be maintained if you are to continue practicing in the CNS role. You can then apply for a medicare provider number and beging billing for your services at 85% of the physician fee! This is probably much more than you were asking but I thought it might help you.