This text explains reliability issues in microelectronics systems manufacturing and software development with an emphasis on evolving manufacturing technology for the semiconductor industry. Since most microelectronics components have an infant mortality period of about one year under ordinary operating conditions, and many modern systems, such as PCs, are heavily used in the first few years, the reliability problem in the infant mortality period becomes extremely important. Burn-in is an accelerated screening procedure that eliminates infant mortalities early on in the shop before shipping out the products to the customers. This book should also help readers to analyze systems that exhibit high failure rate during a long infant mortality period. The text presents ways to systematically analyze burn-in policy at the component, sub-system, and system levels. Various statistical methods are addressed including parametric, nonparametric, and Bayesian approaches. Many case studies are introduced in combination with the developed theories. Included in the book is an introduction to software reliability. The book should help manufacturers and system designers to understand and to design a more reliable product given constraints specified by the users and designers. An understanding of the infant mortality period may solve many reliability problems, including those faced in the semiconductor industry and software industry.