In  this book,  we  will  exam  the  underlying  digital  technologies required to  build  the  digital  economy. We will  also  discuss basicconcepts and elements of the technologies that makea digital economy possible and how they work. We will lookat some of the major applications. We will look into the twomost  important  aspects  of  the  economy:  the  financialindustry  (Fintech) and  the manufacturing  industry  (Industry4.0).  This  subject  is  vast  and  is  quickly  changing.  It  isimpossible  to  cover  the  subject  entirely  in  one  book.  Thisbook  serves  as  a  comprehensive  introduction  andbackground  to  anyone  who  is  interested  in  the  subject  inorder  to  do  further  research  on  the  individual  subjectsincluded  here. Many  references  are  cited  in  the  interest  ofresearch and further exploration. And to conclude the book,we  will  discuss  how  the  economy  and  society  as  a  wholemay be transformed in the next 20 or 30 years.Len Mei, Ph.D.March 2022