In this tenth chapter we address the impact of external flows on cell locomotion. We start by considering the dynamics of spherical swimmers in arbitrary external flows. In this case, the impact on cell translation and rotation can be obtained exactly (Faxén's laws), which we then use to address cell trajectories in simple canonical flows. We next examine the case of elongated swimmers, which may be analysed when the flow is linear, a limit relevant to many situations where the typical length scale over which the flow varies is much larger than the size of the organism. For slender swimmer shapes, we derive a simplified version of Jeffery's exact equation for ellipsoids in linear flows. Jeffery's equation is then used, in agreement with experiments, to characterise the angular dynamics of elongated bodies in shear flows and address the trajectories of elongated swimmers in elementary flows. We finally consider the case where swimmers have a preferential swimming direction, modelled by an additional external torque, which may then lead to cell trapping in high-shear regions and to hydrodynamic focusing.