The Exponential distribution, discussed in the previous chapter, assumes a constant failure rate that sometimes fails to represent field data. In practice, failure rates can vary—decreasing, increasing, or exhibiting complex patterns with multiple peaks. A non-constant failure rate is more realistic, as many products, especially in the wear-out phase, typically show an increasing failure rate. Consequently, a more flexible statistical distribution is needed to model such behavior. The Weibull distribution, widely used in reliability engineering, meets this need due to its versatility. This chapter examines the statistical properties of the Weibull distribution and explains how it can be effectively applied to reliability analysis.