The book covers material contained in several courses of Curriculum 68 as described by the Association of Computing Machimery (ACM). This text is self-sufficient in that there are enough details for 370 and PL/I to support the rest of material and it will be useful for graduate students as well as professionals . In addition to discussing the traditional system components of assemblers and macros, the book gives special emphasis to important features of systems programming presently not covered in many texts-compilers, the advanced problems of storage allocation, recursion, operating systems, and I/O programming.