Compartmentalization of biochemical processes is essential for cell function. Although membrane‐bound organelles are well studied in this context, recent work has shown that phase separation is a key contributor to cellular compartmentalization through the formation of liquid‐like membraneless organelles (MLOs). In this Minireview, the key mechanistic concepts that underlie MLO dynamics and function are first briefly discussed, including the relevant noncovalent interaction chemistry and polymer physical chemistry. Next, a few examples of MLOs and relevant proteins are given, along with their functions, which highlight the relevance of the above concepts. The developing area of active matter and non‐equilibrium systems, which can give rise to unexpected effects in fluctuating cellular conditions, are also discussed. Finally, our thoughts for emerging and future directions in the field are discussed, including in vitro and in vivo studies of MLO physical chemistry and function. Phase separation and active matter: Liquid–liquid phase separation has been shown to play a major role in compartmentalization of cellular biochemistry. The key conceptual and mechanistic underpinnings of this phenomenon, including weak noncovalent interactions and polymer physics principles, and biological examples are discussed.