Gas-liquid and liquid-vapor pipe flows in microgravity have been studied for more than forty years because of theirpotential applications in space industries for thermal control of satellites, propellant supply for launchers, and wastewater treatment for space missions. Also, microgravity experiments provide unique conditions for highlighting and modeling capillary and inertia effects in the dynamics of two-phase flows. This paper discusses the results of flow pattern characterization, void fraction measurements, wall and interfacial shear stresses, and heat transfer coefficients. The main results are compared with ground experiments and classical correlations and models from the literature. Recent results from flow boiling in pipes are also discussed and perspectives on future studies are presented.