Both individual-based models and PDE models have been developed to de-scribed the active movement of cell populations in various contexts. Individual-based models can faithfully replicate the detailed mechanisms of cell signaling andmovement but are computationally intensive. PDE models are amenable for fastcomputation and mathematical analysis but are often based on phenomenologicaldescriptions of macroscopic cell fluxes. Multiscale methods must be developed toelucidate the connections between individual-based models and PDE models in or-der to combine the strengths of these approaches. This chapter summarizes recentprogress in connecting individual-based models and PDE models for chemotaxis ofbacterial populations, which is a classic example for multiscale modeling in biol-ogy. The application scope and limitations of the Keller-Segel chemotaxis equationis also discussed.