Information Systems / Information Technology (IS/IT) Satisfaction is a key indicator of IS/IT success. For IS professionals and providers, satisfaction is critical throughout the life of a system because dissatisfied stakeholders can derail implementation, discontinue using an important system, erode IS/IT budgets, or even transfer their entire IT infrastructure to a different organization. The IS literature offers several perspectives on satisfaction, but none yet accounts fully for known satisfaction phenomena. We identify ten observed satisfaction effects, and summarize six existing models for satisfaction, identifying their merits, and the limits of their explanatory power. We then advance Yield Shift Theory (YST), a new causal theory for the satisfaction response that offers a more complete explanation of this phenomenon. YST derives two propositions from five assumptions to propose that variations in the satisfaction response are caused by shifts in yield for an individual's active goal set. We argue the falsifiability and scientific utility of the theory, discuss its relevance to the IS/IT artifact, and suggest a variety of directions for future research.