Despite the obvious practical significance of extratropical transition to subtropical and middle latitude climates, the process of transition remains a black box. Further, operational forecasts of transition are notoriously inaccurate. Forecasted regions of flooding rains and damaging winds (both offshore and inland) are often inadequate (e.g. Fran, 1996; Hugo, 1989). Conventional methods for determining the point of transition occasionally fail, such as: reversal of cyclone central temperature anomaly; lack of cyclone central deep convection; loss of an eye structure; dramatically increasing radius of maximum winds. Using a synthesis of observations, reanalyses, and high-resolution (1-10km) mesoscale model (MM5) simulations, we will discuss a conceptual model for transition. We will examine the significant (but not necessary) role of midlatitude troughs, the importance of a gradient of water temperature,and factors that control post-transition intensity change.