Research conducted since the construct of leader-member exchange (LMX) was first investigated in 1972 is reviewed with respect to the theoretical, measurement, and analytic adequacy of LMX studies. It is shown that conceptual definitions of LMX and its subdimensions have evolved over time, often with little reason or rationale given for changes. Likewise, the measures employed to assess LMX have varied widely and have included an almost bewildering array of diverse item content. Finally, LMX research has rarely examined the level of analysis at which its findings hold. All of these shortcomings lead to the conclusion that we may know less than we should about fundamental leader-member exchange processes and that future research must be conducted with greater attention devoted to the key issues outlined in this review.