This paper presents an object-oriented textual language designed to specify programmable logic controller software. This methodology, called OOST, allows users to specify the control logic in a natural manner, using a collection of objects that represent machines and other devices within a manufacturing system. The object-oriented specification technique may be used during the whole control software life cycle, and could be considered as a requirement definition language or an implementation one. An automatic PLC program generation system that uses descriptions written in OOST is also presented. A brief literature review is presented and the implementation details are discussed. The final part presents some future improvements and a few remarks.