The Accretion Process on Protostars

The process of mass accretion onto Young Stellar Objects (YSOs) plays a fundamental role in determining the final stellar mass and setting the initial conditions for planet formation. Despite its critical role, our understanding of accretion remains fragmented, particularly for what concerns the earliest, protostellar phases (Class 0/I). While the community has consolidated a comprehensive knowledge of the accretion process of the later-stage Classical T Tauri Stars (CTTSs), a similar level of understanding is critically lacking for the protostellar phase, where the bulk of the mass is assembled. This work aims to review recent major results, both from the observational and numerical point of view, bridging the gap between the two approaches and providing an updated, complete assessment of accretion in protostellar sources. We present different techniques to measure accretion on protostars, analyze how methodological differences affect parameter estimation, discuss the caveats in comparing with numerical models, and suggest the next steps to take towards an ever more exhaustive picture of the protostellar phase.