Investment decisions are crucial for maximizing financial outcomes and allocating capital effectively in financial markets. Net Present Value (NPV) and Internal Rate of Return (IRR) are two widely used methods in investment appraisal. This paper explores the distinctions between these two methods, focusing on their theoretical underpinnings, practical applications, and limitations in real-world scenarios. Through a series of hypothetical case studies, the paper demonstrates how NPV and IRR perform under different investment conditions, including varying cash flow structures and project sizes. The findings highlight that while IRR provides a percentage return which is easy to interpret, it suffers from limitations such as multiple IRR solutions in projects with non-conventional cash flows. In contrast, NPV offers a more reliable and consistent measure of project value, aligning with the principle of shareholder wealth maximization. The study concludes that NPV is the preferred method for investment evaluation, particularly in projects with complex or irregular cash flows. While IRR remains useful in simpler scenarios, its shortcomings emphasize the need for a more comprehensive approach to capital budgeting decisions.