Abstract This paper is concerned with examination of jet streams, their number, nature, energy relationships, fluctuating location, and steering effect upon extra-tropical cyclones. Jet streams are analyzed in the context of a series of waves, in the upper-level zonal westerlies, that vary in length and oscillate between high and low-index stages. Features of special significance are: (1) a jet stream need not be accompanied by a surface cyclonic system, but the latter presupposes presence of the former; (2) the cyclonic system is one of the two major energy sources in the scheme of mid-latitude circulation; and (3) the transfers of angular momentum, water vapor, heat, and energy required to balance the global budget are accomplished, in part, by migratory eddies associated with wave motions aloft.