The Brahma-siddhi, 'The Demonstration of Brahman' is Mandana Misra's largest work, his most important and the sole one dedicated as a whole to Vedanta. The topics occurring in the doctrine of this work which the present author intends to study here in this book are inter-related; they all have to deal with the nature and functioning of error, whether every-day error or the transcendental error, avidya, which makes us see the multiplicity of phenomena where there is nothing but the utter oneness of brahman. Thet also demonstrate the number of different sources upon which Mandana depended in erecting his own system. In spite of the number and variety of these sources Mandana created a system, the closed coherence of whose parts is a cause of admiration, even if one does not always accept his conclusions.Two appendices are also added to give a glimpse of Mandana Misra's date and his order of works. An exhaustive bibliography has been provided to facilitate the curiosity of readers. An index of important words has also been given.