A wide variety of synthetic molecular machines has been designed and synthesized to construct nanometer-scale assemblies whose molecular motions can be precisely controlled by external stimuli. A helical structure is one of the most intriguing structural motifs to realize such molecular machines, because of its unique spring-like shape that enables reversible extension and contraction motions. This short review highlights the recent progress in the synthesis, structures, and functions of synthetic molecular springs based on single- and multi-stranded helical structures.