Transport studies of two-dimensional electron systems compose two fundamental effects: disorder scattering and electron-electron interaction. Fifty years after Anderson's theory of localization for non-interacting electrons, the question on whether and how electron-electron interaction qualitatively alters the manybody states is still unsettled. The most prominent interaction-driven phenomenon is the Wigner crystallization (WC) of charges. Such a fascinating quantum state of matter (with spin ordering) can be utilized for futuristic applications including quantum electronics and spintronics. The classical version of the WC, with the Coulomb energy less than the Debye temperature, has been demonstrated in electrons on a helium surface. On the other hand, the more desired quantum version, with a Coulomb energy much less than the Debye temperature, has not been previously observed in a zero magnetic field. This colloquia reviews important progress made over the past four decades as understandings of the interplay of disorder and interaction are developed. Recent experimental results we obtained from measuring a novel type of ultra-high purity semiconductor systems will be presented as evidence for interaction-driven nature of the manybody states, including a threshold transport characteristic as a probable evidence of a quantum Wigner Crystal.