The sequence of the human genome provides a scaffold on which numerous annotations, such the locations of genes, can be laid. Genome browsers have been created to allow the simultaneous display of multiple annotations within a graphical interface. In addition, they provide the ability to search for markers and sequences, to extract annotations for specific regions or for the whole genome and to act as a central starting point for genomic research. This review describes the basic functionality of genome browsers and compares three of them: the University of California Santa Cruz (UCSC) Genome Browser, the Ensembl Genome Browser and the NCBI MapViewer.