This study formulates and/or utilizes some models for migration, age at marriage, marriage migration, and child mortality. Furthermore, the study focuses on some motivation factors of migration, trends and determinants of age at marriage, factors influencing consanguineous marriages, determinants and patterns of infant and child mortality, and effect of elimination of some diseases on life expectancy. The inflated geometric distribution describes well the distribution of households for the male migrants aged 15 years & above. The Lee''s theory was acceptable for Bangladesh to describe the volume and diversity of out-migration. The urban population and area were dominant factors for the volume of out-migration identified by the single origin and multiple destinations models. An upward trend in average age at marriage was observed and education, occupation, religion, birth year were the significant factors for female age at marriage. Type I extreme value distribution, Pareto- Exponential model and finite range model were found suitable to describe the distribution of female age at marriage, marriage distance and infant deaths respectively.