Active Streams introduces a middleware framework for building adaptive distributed applications capable of operating in large, heterogeneous, and resource-variable environments. The approach models systems around applications, services, and self-describing data streams enhanced with streamlets—small, location-independent functional units that can be dynamically deployed, tuned, or replaced as conditions change. By combining component-based extensibility with dynamic code generation, Active Streams enables both coarse-grained evolution and fine-grained adaptation across diverse execution contexts. A push-based resource monitoring service supports continuous awareness of system state, while a proactive directory service provides publish/subscribe updates on relevant objects. Together, these mechanisms allow applications and services to respond fluidly to variations in demand and resource availability, simplifying the development of adaptive, data-intensive distributed systems.