One-dimensional (1D) nanoscale objects abundant in nature commonly possess hierarchical structures and are generally constructed via bottom-up self-assembly strategies. The unique high aspect ratio morphology of the assembled nanofibrillar materials, such as collagen, cellulose, and silk, together with highly ordered architectures, endows a range of remarkable functionalities in nature. Inspired by this hierarchical building principle, block copolymers (BCPs) have been developed and employed to engineer man-made functional 1D nanostructures and as models to study the self-assembly process. The rapid development of advanced polymerization techniques allows for the precise design of BCPs and the resulting assemblies with intensive studies on distinct structure–property–function relationships. In this Review, we summarize and discuss the formation of fiber-like micelles from the perspectives of fundamental driving forces and molecular interactions involved in the solution self-assembly process. Three main formation mechanisms are highlighted, including covalent bonding, volume exclusion, and crystallization, which are involved in the corresponding domains of coronal, interfacial, and core segments of BCPs. Two spatiotemporal levels of fiber-like assemblies are discussed. In addition, the emerging applications and a general guidance for the rational design of advanced BCPs are proposed in light of the unique traits of fiber-like micelles.