Next-generation sequencing technologies have greatly reduced the cost of sequencing genomes. With the current sequencing technology, a genome is broken into fragments and sequenced, producing millions of "reads." A computer algorithm pieces these reads together in the genome assembly process. PHAST is a set of online modules (http://gcat.davidson.edu/phast) designed to teach advanced high school and college students the genome assembly process. PHAST allows users to assemble phage genomes in real time and includes tutorials detailing the complexities of genome assembly. With PHAST, students learn concepts behind genome assembly and understand how mathematics solves biological problems such as genome assembly.