Why did Operation MARKET GARDEN fail? Was it due to poor decision making, faulty planning, or bad intelligence? After outlining the operation's plan and objectives, this paper evaluates several theories about one of the most famous military failures of World War II. Each theory is examined in light of historical records and biographical accounts that detail what MARKET GARDEN planners and commanders knew, and when they knew it. The paper concludes that, while intelligence analysts could have done a better job, it is unfair for them to shoulder most of the blame. Strategic and operational planners were also at fault for pressing forward with the operation, in spite of known risks, in order to test airborne operations before the war ended. Furthermore, Field Marshal Montgomery, the operational commander, must take responsibility for dismissing intelligence reports that contradicted his situation assessment and challenged the wisdom of his decision to execute Operation MARKET GARDEN as planned.