This document summarizes renewable energy certificate (REC) mechanisms in several countries including India, Japan, the UK, and Australia. It notes that these countries have among the most robust REC systems globally. It provides details on the REC trading prices, volumes, validity periods, renewable portfolio standard obligations, penalties for non-compliance, and other aspects of the REC systems in each country. It concludes by highlighting some lessons for India to improve enforcement of its renewable portfolio standards and increase incentives for compliance through its REC program, such as by incorporating differential penalties, increasing the validity and trading windows for RECs, and ensuring long-term price stability.