The field of automotive engineering has seen an explosion in the presence of on-board electronic components and systems vehicles since the 1970s. This growth was initially motivated by the introduction of emissions regulations that led to the widespread application of electronic engine controls. A secondary but important consequence of these developments was the adoption of on-board diagnostics regulations aimed at insuring that emission control systems would operate as intended for a prescribed period of time (or vehicle mileage). In addition, the presence of micro-controllers on-board the vehicle has led to a proliferation of other functions related to safety and customer convenience, and implemented through electronic systems and related software, thus creating the need for more sophisticated on-board diagnostics. Today, a significant percentage of the software code in an automobile is devoted to diagnostic functions. This paper presents an overview of diagnostic needs and requirements in the automotive industry, illustrates some of the challenges that are associated with satisfying these requirements, and proposes some future directions.