This book gives an understanding of Fundamentals of Computers and BASIC programming language. Fundamentals of computer are very important in any discipline of computer studies. This book consists of two parts, the first part is Business Data Processing and the second is BASIC programming language. These parts are collected from different books on fundamentals of computers and BASIC language, and from computer Journals and Magazines for the benefit of the students. This is prepared as a text for the B.D.P course of the B.Com.(Hons.) of the University of Delhi and for the B.B.A course of Royal University of Bhutan. Today data processing courses are offered in almost all Colleges, Universities, Institutes of business and vocational studies, and in high schools. We hope this book uses to students aspiring to learn fundamentals of the computers and BASIC language.