MCTB The Four Noble Truths
The Four Noble Truths, suffering, its cause, its end, and the path that leads to its end, are fundamental to the teachings of the Buddha. He was fond of summarizing his whole teaching in terms of them. Actually, when asked to be really concise, he would just say the first and third: suffering and the end of suffering. This was what he taught. Like the other little lists here, they have great profundity on many levels and are worth exploring in depth.