This paper discusses practical development of business rules (BR) systems. The main conceptual foundations of BR are discussed, and selected tools for BR design and implementation are described. An application of a rule-based systems design tool (Mirella Designer) for BR design is proposed. Business rules visual representation using XTT in Mirella Designer is both transparent and compact. The underlying logical formulation of XTT opens up possibility of formal analysis and refinement performed on-line, during the design.