An electrochemical DNA biosensor is a device that utilizes the inherent ability of two complementary strands of nucleic acids to form a double helix. The specificity of this reaction, namely hybridization, is used in the detection of target DNA sequences with a view toward developing point-of-care devices. Since the early 1990s, great progress has been made in this field, but there are still numerous challenges to overcome. This chapter describes the components of an electrochemical DNA biosensor for researchers new to the field, paying particular attention to intercalator-based DNA biosensors. We will use a well-defined electro-active DNA intercalator Hoechst 33258, as our running example. Two of the most classic DNA sensing methods: solution-based and surface-immobilized methods are discussed, along with guiding notes that would help identify and overcome possible problems in a typical electrochemical DNA biosensor experiment.