With the number of clock domains increasing in today’s complex ASIC designs, the ability to thoroughly verify clock domain crossings (CDC) has become even more important. As in functional verification, to ensure CDC issues are thoroughly verified, a comprehensive test plan is essential. Based on our experience working with many customers, we developed a five-step planning process for CDC verification. After having a CDC test plan, an effective CDC verification methodology should include structural, protocol, and metastability verification. This ensures that CDC signals are handled reliably at the design stage, avoiding costly respins after they are fabricated.