Determining what testing is required for the development and approval of a new medical device can be a complex issue. This is even more the case after the issue of when to perform necessary tests is factored in. Essentially, if one or more clinical trials (with enabling IDE) is part of the development scheme, exactly how much biocompatability work must be conducted prior to the IDE filing is not a fixed or well-defined list. Post approval, one must determine what ongoing testing is required to ensure continued safety of the product. Understanding the complexities requires careful consideration of some key concepts.