Scientific computing is moving rapidly from a world of “reliable, secure parallel systems” to a world of distributed software, virtual organizations and high-performance, though unreliable parallel systems with few guarantees of availability and quality of service. This transformation poses daunting scaling and reliability challenges and necessitates new approaches to collaboration, software development, performance measurement, system reliability and coordination. This paper describes Renaissance approaches to solving some of today's most challenging scientific and societal problems using Grids and parallel systems, supported by rich tools for performance analysis, reliability assessment and workflow management.