The Flex 4 ACE (Adobe Certified Experts) Exam is based upon the most critical job activities that a Flex developer performs. The skills and knowledge certified by this examination represent a professional level of expertise for a certified individual.

Flex 4 ACE Exam is $150 (U.S.)..

Adobe provides guidelines and sample questions for the exam in a downloadable PDF document:
Flex 4 ACE Exam Preparation Guide (PDF, 20K).

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To become certified, you must pass a challenging exam that consists of 50 multiple-choice questions.