This review discusses the intriguing family of natively unfolded proteins, which challenges the traditional protein structure-function paradigm. Intrinsically unfolded proteins do not possess uniform structural properties and can be divided into two structurally different groups: intrinsic coils and premolten globules. Intrinsic coils have hydrodynamic dimensions typical of random coils in poor solvents and lack ordered secondary structure, while premolten globules are more compact and exhibit some residual secondary structure. These proteins undergo disorder-order transitions during or before their biological function. The Protein Quartet model, which includes four specific conformations (ordered forms, molten globules, premolten globules, and random coils), is proposed to explain the function of these proteins. The review also highlights the functional importance of intrinsic disorder, including increased plasticity for effective molecular recognition and the ability to undergo disorder-order transitions. Experimental evidence for function-related transitions between these conformations is provided, emphasizing the dynamic nature of natively unfolded proteins.This review discusses the intriguing family of natively unfolded proteins, which challenges the traditional protein structure-function paradigm. Intrinsically unfolded proteins do not possess uniform structural properties and can be divided into two structurally different groups: intrinsic coils and premolten globules. Intrinsic coils have hydrodynamic dimensions typical of random coils in poor solvents and lack ordered secondary structure, while premolten globules are more compact and exhibit some residual secondary structure. These proteins undergo disorder-order transitions during or before their biological function. The Protein Quartet model, which includes four specific conformations (ordered forms, molten globules, premolten globules, and random coils), is proposed to explain the function of these proteins. The review also highlights the functional importance of intrinsic disorder, including increased plasticity for effective molecular recognition and the ability to undergo disorder-order transitions. Experimental evidence for function-related transitions between these conformations is provided, emphasizing the dynamic nature of natively unfolded proteins.