The SNOBOL4 programming language was developed by Griswold, Poage and Polonski (1). It combines facilities available in problem oriented languages with string manipulation facilities, pattern matching facilities and facilities for compilation during execution. The present description attempts to accomplish three objectives. It is an introduction to SNOBOL4 for the programmer with previous programming experience in some programming language but not necessarily previous experience with SNOBOL3. It is intended also to provide dynamic insights into the mechanisms for statement execution, and to describe source language structures in terms of the information structures to which they give rise during execution. It is felt that dynaamic insights into the way in which source statements are executed help not only the system programmer but also the average user. This description is based on reference 1 and on two very worthwhile days of discussion with the authors of SNOBOL4 at Holmdel. The author is indebted also to John Kelly for fruitful discussion of aspects of SNOBOL4 and for proofreading the manuscript.