System Integration for IEC 61850 is the branch of Systems Engineering for combining smaller components of a subsystem to function as a comprehensive system on a shared network. This includes new and existing hardware, software and communications for the distribution of data between disparate subsystems. This process can be developed after the creation of a System Specification using a Top-down Engineering approach or a combination of Top Down and Bottom Up Engineering approaches. System Integration can also be completed without a System Specification using the Bottom up Engineering Approach. Typically a high level of innovation, flexibility and problem solving is essential for success when integrating a system lacking a developed System Specification.