Business Process Modelling Notation (BPMN) intends to bridge the gap between business process design and implementation. Previously we provided a process semantics to a subset of BPMN in the language of Communicating Sequential Processes (CSP). This semantics allows developers to formally analyse and compare BPMN diagrams using CSP’s traces and failures refinements. In this paper we introduce a comprehensive set of operations for constructing BPMN diagrams, provide them a CSP semantics, and characterise the conditions under which the operations are monotonic with respect to CSP refinements, thereby allowing compositional development of business processes.