In this chapter, a few software architectures and platforms are discussed in relation with their ability to cope with business integration problems in large, geographically dispersed companies. Of these architectures, the three-tier architecture has reached maturity and proved its usefulness in solving these problems. As an illustration of its usefulness, two successful applications of the three-tier architecture, based on Java 2 Platform Enterprise Edition (J2EE), solving business integration problems inherent to investment decision-making in large companies, Framework for Investment Decision Support (FIDES) and ProjectsAnywhere, are described in detail. For solving more complex business integration problems, Service Oriented Architecture (SOA), based on agent or Web services approach, is recommended. Hopefully, this chapter will provide concise information about architectures and platforms, and an insight into two complex applications based on them, that will be useful in developing other complex applications that face similar business integration problems.