This paper discusses the importance of the cost of capital and its impact on the performance of firms in Kenya. The cost of capital is affected by various factors such as interest rates, inflation, market conditions, and government policies. Financial managers use discounting cash flow techniques to evaluate capital investments, which requires the estimation of the project's cash flows and the discount rate. The article also explores the concept of capital structure and its significance in determining the cost of capital. Managers need to manage the capital structure effectively to optimize shareholder wealth and minimize the company's cost of capital. The article highlights the importance of balancing the mix of financing sources between debt and equity. High costs of capital can limit a firm's access to financing, while low costs of capital can improve a firm's investment and growth opportunities. This article concludes that the cost of capital is an essential factor that affects the performance of firms in Kenya. It impacts investment decisions, financial structure, and competitiveness in the market. Researchers suggest that managers should balance the use of debt and equity financing in an optimum manner to maximize shareholder wealth. However, the research suggests that high costs of capital can discourage firms from investing in new projects, reducing growth and profitability. Firms need to evaluate their cost of capital and consider strategies to lower it, such as improving creditworthiness or exploring alternative financing options.