The domestic dog represents one of the most dramatic long-term evolutionary experiments undertaken by humans. From a large wolf-like progenitor, unparalleled diversity in phenotype and behaviour has developed in dogs, providing a model for understanding the developmental and genomic mechanisms of diversification. We discuss pattern and process in domestication, beginning with general findings about early domestication and problems in documenting selection at the genomic level. Furthermore, we summarize genotype-phenotype studies based first on single nucleotide polymorphism (SNP) genotyping and then with whole-genome data and show how an understanding of evolution informs topics as different as human history, adaptive and deleterious variation, morphological development, ageing, cancer and behaviour.