Motor proteins are enzymes that accomplish mechanical work in a wide variety of biological processes. In this review we focus on bulk and single molecule methods to study how motor proteins function. We discuss in detail the analysis of the motor protein DnaB, a hexameric helicase that unwinds DNA at a replication fork in Gram-negative bacteria. Bulk and single-molecule studies have complemented one another to arrive at a comprehensive mechanistic view of how DnaB unwinds double-stranded DNA.