Methods and strategies for estimating children mortality, adult mortality, and age-specific mortality and life expectancy in population of global, regional, and country levels are an important part of the Global Burden of Disease (GBD) study and are the starting point and foundation of the GBD study. The first section of this chapter introduced the sources of mortality data, indirect techniques for demographic estimations, organizations for global demographic statistics, and the status of mortality statistics. The second, third, and fourth sections of this chapter described the methods for the estimation of child mortality, adult motality, age-specific mortality, and life expectancy in populations, respectively. Highlights of the GBD study’s estimation of the under-5 mortality rate (U5MR) include (1) to improve indirect techniques for the analysis of summary birth history (SBH) data to reduce bias and measurement error and (2) to enhance the validity of child mortality probability (5q0) prediction with meta-analysis of data from multiple sources and the spatiotemporal Gaussian process regression (ST-GPR). Highlights of the GBD study’s estimation of adult mortality include (1) optimizing the death distribution method (DDM) to use large-scale imperfect vital registration data and (2) developing the corrected sibling survival (CSS) method to improve the accuracy of estimates of adult mortality using sibling survival data. Also as with the estimation of 5q0, a new ST-GPR is used to model the empirical data to estimate 45q15. Highlights of the GBD study’s estimation of age-specific mortality pattern are to develop Mortified Logit Life Table (MLLT) and Model Life Table system with flexible standards (MLTFS) based on expanding Brass’s “Logit Model Life Table System.” Section 3.5 compares the strengths and weaknesses of the GBD estimates with other similar estimates and discusses the implications of the GBD mortality estimates methods.