This review article by A. Schneemann, V. Bon, I. Schwedler, I. Senkovska, S. Kaskel, and R. A. Fischer provides an in-depth analysis of flexible metal-organic frameworks (MOFs), also known as soft porous crystals. The authors cover the literature from 2009 to 2013, highlighting the recent progress in understanding and controlling the structural transformability of these materials. Flexible MOFs combine crystalline order with cooperative structural changes, allowing them to respond to various physical and chemical stimuli in a tunable manner. Key properties include breathing and swelling phenomena, triggered by guest adsorption/desorption, photochemical, thermal, and mechanical stimuli. The review also discusses linker rotation and sub-net sliding, which are other important flexible properties. Recent advancements in in situ characterization techniques and theoretical approaches to understand breathing mechanisms and phase transitions are emphasized. The article categorizes flexible MOF systems based on the type of metal nodes and their coordination chemistry with linker molecules, and explores the potential applications of these materials in separation, catalysis, sensing, and biomedicine.This review article by A. Schneemann, V. Bon, I. Schwedler, I. Senkovska, S. Kaskel, and R. A. Fischer provides an in-depth analysis of flexible metal-organic frameworks (MOFs), also known as soft porous crystals. The authors cover the literature from 2009 to 2013, highlighting the recent progress in understanding and controlling the structural transformability of these materials. Flexible MOFs combine crystalline order with cooperative structural changes, allowing them to respond to various physical and chemical stimuli in a tunable manner. Key properties include breathing and swelling phenomena, triggered by guest adsorption/desorption, photochemical, thermal, and mechanical stimuli. The review also discusses linker rotation and sub-net sliding, which are other important flexible properties. Recent advancements in in situ characterization techniques and theoretical approaches to understand breathing mechanisms and phase transitions are emphasized. The article categorizes flexible MOF systems based on the type of metal nodes and their coordination chemistry with linker molecules, and explores the potential applications of these materials in separation, catalysis, sensing, and biomedicine.