Since the start of seed and other market reforms in the 1990s, the annual number of improved varietal releases for maize in Kenya has increased substantially. Reforms have resulted in not only private firms entering the market and releasing improved varieties, but also an increase in varietal releases by the public sector. This paper reviews some of the key policy reforms related to maize in Kenya, their impacts on varietal development and yields.We present a yield model to relate national maize yields with a number of exogenous factors, that have policy oriented effects associated with significant impact on yields. We use a number of policy variables such as public R&D, the number of Plant Breeder s Rights issued, and the years since private varieties have been introduced as instrument variables that influence new varietal releases directly, and yields indirectly. We find that the number of improved maize varieties released and the share of area under improved varieties have no impact on maize yields. We argue that this is because farmers continue to use older improved varieties, and that newer improved varieties may not have the assumed yield advantage and/or are not as widely adopted to have the desired yield impact. Acknowledgement :