For elementary, original source material on the Dhamma, two compilations by the great German scholar-monk Nyanatiloka Thera (Ven. Nyanaponika's teacher) are still unsurpassed. The more elementary is "The Word of the Buddha", first compiled in 1906 and subject to some sixteen reprints. This book arranges the Buddha's sayings around the framework of the Four Noble Truths. The more advanced title is "The Buddha’s Path to Deliverance", which documents the Buddha's own instructions on all the different methods of meditation, both for concentration and insight, and arranges them according to the pattern of the seven stages of purification.