This book was compiled from writings by Hari Prasad Shastri, who devoted his life to the study and propagation of the non-dual teachings and their application through the Yoga of Self-Knowledge, Adhyatma Yoga. After receiving instruction from illumined sages in Northern India and confirming the essential teachings of the Upanishads in his own experience, he travelled in Japan, China and Europe and studied the classics of the world's wisdom traditions. In 1933, in London, he founded Shanti Sadan as a traditional centre of non-duality and the way of Self-Knowledge. Meditation Its Theory and Practice was one of the first books published by Shanti Sadan. It contains a distillation of insights and guidance in meditation as it is understood and practised in the non-dual schools, with special relevance for those who wish to seriously practise meditation without having adopted discipleship under a particular teacher. In the current edition, the original content has been somewhat re-arranged and augmented by clearly structured sets of meditation exercises that may be taken up for regular daily practice.