This review provides an overview of the progress in observations of large-scale star formation, focusing on the interface between extragalactic and Galactic studies. It discusses methods for measuring gas contents and star formation rates (SFRs) and updates prescriptions for calculating SFRs. The review covers relations between star formation and gas on scales ranging from entire galaxies to individual molecular clouds. Key topics include the hierarchy of physical processes involved in star formation, the role of dust as a tracer of the interstellar medium (ISM), and the use of molecular gas tracers such as carbon monoxide (CO). The review also addresses the mass functions of stars, clusters, and gas structures, and highlights the importance of understanding the coupling between processes at different scales. The authors emphasize the need for a unified approach to studying star formation, incorporating both observational and theoretical insights.This review provides an overview of the progress in observations of large-scale star formation, focusing on the interface between extragalactic and Galactic studies. It discusses methods for measuring gas contents and star formation rates (SFRs) and updates prescriptions for calculating SFRs. The review covers relations between star formation and gas on scales ranging from entire galaxies to individual molecular clouds. Key topics include the hierarchy of physical processes involved in star formation, the role of dust as a tracer of the interstellar medium (ISM), and the use of molecular gas tracers such as carbon monoxide (CO). The review also addresses the mass functions of stars, clusters, and gas structures, and highlights the importance of understanding the coupling between processes at different scales. The authors emphasize the need for a unified approach to studying star formation, incorporating both observational and theoretical insights.