Covalent organic frameworks (COFs) are promising crystalline porous materials with highly tunable structures and functionalities. In the last decade, COF films have been synthesized and used as multifunctional materials for a diverse range of separation applications. However, there are still challenges in the scaling-up preparation of COF films with benchmarked performance for precise molecular separations. Recently, research has turned its attention to preparing functional COF films with an appropriate aperture size/functionality, facile preparation process, and superior stability. In this Perspective, we outline the recent advances in designing and preparing functional COF films based on surface and interfacial chemistry. On top of that, current obstacles and opportunities in the scaling-up preparation of functional COF films and their industrial applications are proposed and discussed. This Perspective strives to inspire the development of functional COF films with tailored structures and functionalities and promote their practical applications in diverse molecular separation processes.