This document discusses random mating and non-random mating in populations. It describes assortative mating where individuals mate with similar partners, and disassortative mating where individuals mate with dissimilar partners. The effects of these on genotype frequencies are explained. The concept of genetic equilibrium is introduced. Inbreeding is discussed for idealized, isolate, and real populations. Formulas are provided for the rate of inbreeding increment under different population structures. Effective population size is also covered as it relates to rates of inbreeding and genetic drift in small populations.