Research in the area of abstract data types started about 20 years ago. Since then there has been continuous activity with strong influence both on the applications and the theoretical foundations of methodologies for software design. The Ninth Workshop on Specification of Abstract Data Types was held jointly with the Fourth COMPASS Workshop in Spain in 1992. The main topics covered were: object-oriented specifications, rewriting methods, specification languages and associated tools, type systems, and algebraic specification of concurrency. This volumes contains four invited papers presented at the workshop together with the final versions of 17 contributed papers selected after a careful refereeing process from 46 submissions.