“What the Buddha Taught” by Walpola Rahula
This classic book presents the teachings of the Buddha in a concise, comprehensive, logical and faithful way. It was first published in 1959 and later expanded, and is considered one of the best, and most readable, sources for gaining an understanding of essential early Buddhist teachings. Please read the expanded 1974 edition, which is available in print form (from Barnes & Nobles, Amazon, and other sources) and also as a free PDF:
Walpola Rahula (1907–1997) was a Buddhist monk, scholar and writer. He is one of the most honored Sri Lankan intellectuals of the 20th century. In 1964, he became the Professor of History and Religions at Northwestern University, thus becoming the first bhikkhu to hold a professorial chair in the Western world. He also once held the position of Vice-Chancellor at the then Vidyodaya University (currently known as the University of Sri Jayewardenepura). He has written extensively about Buddhism in English, French and Sinhalese.