Traffic engineering is a field of science and technology aimed at achieving safe, smooth, and sustainable movement of people and goods. Traffic engineering emerged in the early twentieth century with the spread of internal combustion engine vehicles and developed with the global motorization after World War II. Its initial scope was planning, design, and operation of roads necessary to reduce traffic congestion and accidents caused by automobiles. Now, it deals with a wider range of traffic issues, considering sustainability of people’s mobility, including not only safety and efficiency but also traffic pollution (environmental load) for not only automobiles but also pedestrians, bicycles, and public transportation (such as buses, trams, and LRT). This chapter provides an overview of the techniques to realize smooth and safe road traffic and the methodologies to scientifically analyze and describe the flow caused by the movement of multiple road users (i.e., traffic flow), as the basics of traffic engineering.