This document discusses knowledge-intensive service firms, sectors, and systems. It defines services, service firms, and service sectors. A service system is described as people, technologies, and resources interacting to create mutual value, often within and between firms. The document explores definitions and classifications of knowledge-intensive services, business-related services, and business services. It examines where knowledge exists within these systems and debates different ways to measure and understand knowledge. Sectoral data on workforce skills, technology use, and knowledge development is presented to analyze knowledge intensity across industries.