This document provides an introduction to genome-wide association studies (GWAS) and their role in discovering the genetic basis of complex traits and diseases. It explains that GWAS are a hypothesis-free approach to searching the entire human genome for genetic variants associated with a trait using common single nucleotide polymorphisms. Over 2,000 traits and diseases have been studied through GWAS, identifying over 15,000 genetic associations. The document traces the development of GWAS from early human genome sequencing and projects to characterize human genetic variation to the availability of high-throughput genotyping arrays that enabled widespread application of GWAS in disease research.