IT outsourcing is the use of third-party resources to provide facilities and perform functions/services historically performed by internal IT personnel. Historically, IT organizations have outsourced their service provision to a single managed service provider. In today's competitive marketplace, however, many are focusing on their core activities and relying on the support of a multi-sourcing model. SIAM/MSI - An Introduction to Service Integration and Management/Multi-Sourcing Integration for IT Service Management explores the various characteristics of this IT operating model.