Among self-assembled nanostructures, wormlike micelles (WLMs) have a great potential in many areas of chemistry, biology, and medicine. Direct-imaging cryo-transmission electron microscopy (cryo-TEM) is a powerful tool for acquiring essential structural, dynamic, and kinetic information on these self-assembled nanostructures in their native, hydrated state. The strength of direct-imaging cryo-TEM arises from being able to uniquely provide single-particle analysis, directly, at high resolution, and without the need for post-imaging processing. This is in contrast to, but can well be combined with, information from techniques widely used for quantitative and statistical analysis of nanostructured fluids and micelles e.g. rheology and scattering, which probe solution bulk properties. Furthermore, with cryo-TEM both local and global details are detected. Either subtle changes in the assembly or gross modifications in the morphology and phase can be captured by cryo-TEM, making this method an attractive tool in the investigation and development of interesting self-assembled fluid systems. These advantages have proved instrumental for confirming or disproving hypotheses and models that are otherwise hard, or impossible, to conclusively verify. This chapter summarizes central concepts of direct-imaging cryo-TEM and highlights key contributions of this methodology to unfolding the structure and properties of micellar systems, among them the core-shell structure, swollen end-caps, the second critical micellar concentration, and branching points forming dynamic networks.