Hi,
The short answer is that "it depends." The new expert level certifications do require recertification after a number of years. The time interval may vary. The Associate level exams are typically targeted to a specific version of a product. They do not expire
per se. Instead, when the technology is retired the related exams will no longer be available.
Here is the main page for certificatons. It will help give you an idea about the process.
http://www.microsoft.com/learning/en/us/certification-overview.aspx
What technologies are you interested in? If you give us some details we can help you more specific information. Microsoft has a tool called Learning Plans that help you plot a certification path. Take a look:
http://www.microsoft.com/learning/en/in/training/format-learning-plans.aspx
Mike Corkery, MCT, MVP (Office Systems), MCSD (Windows Store Apps), MCITP, MCPD, MSF, etc. Please do not forget to click “Vote as Helpful” if any post helps you and "Mark as Answer”if it solves the issue.