Science is a passion for facts and a constant and systematic search for truth. It flourishes in an atmosphere of freedom. Such an atmosphere used to exist in ancient India where the passion for truth-seeking could find expression and sustenance. The people of ancient India made immense contributions in the fields of philosophy, religion, pure sciences, and technology, This is the reason why India is considered one of the hotbeds of human civilization which has made enormous contributions to enrich the intellectual heritage of mankind. At the end of the first millennium, India was at the pinnacle of its glory, when the so-called "New World" was not yet discovered and the birth country of the Industrial Revolution was not yet well known to the world. This encyclopedia is the outcome of the sustained work put in for several years by the well-known author Shri. M.S. Sreedharan in collecting, collating, and writing up the information on prevailing ancient sciences in the form of a thesaurus. This work is a glowing tribute to the erudite scholarship of the author, who is not amidst us anymore. This book will be a great guide and source of inspiration for the readers, especially the youth of India.