This paper presents a methodology for business process modelling. The methodology recognizes and separates logical and physical models of business processes. The Logical Model represents collection of fundamental and atomic business functions (activities) mostly independent of organisational and technological constraints. The Physical Model, in the context of the given organisational and technological environment, defines a business process as a thread of specific implementations of specified fundamental activities. Structured System Analysis is used as a tool for logical business process modelling and Activity Diagrams as a tool for physical business process modelling.