This chapter provides a brief overview of dataflow, including concepts, languages, historical architectures, and recent architectures. It is to serve as an introduction to and summary of the development of the dataflow paradigm during the past 45 years. Dataflow has inherent advantages in concurrency, synchronization, and speculation over control flow or imperative implementations. However, dataflow has its own set of challenges to efficient implementations. This chapter will address the advantages and challenges of dataflow to set a context for the remainder of this issue.