This text aims to provide an understanding of the basic principles of electronics related to the communication, control and computer systems which affect life. Practical applications of the subject are considered throughout, and actual devices and their uses are described, to encourage the reader to "do" some electronics. Mathematical requirements have been kept to a minimum. The book is not based on any single syllabus but is suitable for students taking BTEC units Electronics NII and NIII, City and Guilds Electronics Servicing (course 2240), GCSE and A'Level course, and short courses in further and higher education. This second chapter has been updated with additions to certain chapters, particularly those on digital systems and computing.