This document provides a more comprehensive and complete impact assessment of the introduction of Universal Credit. Universal Credit is expected to be introduced in October 2013, and individuals will be migrated to Universal Credit over the subsequent four years. The policy will restructure the benefit system, to create one single income-replacement benefit for working age adults which unifies the current system of means-tested out of work benefits, tax credits and support for housing. It will improve work incentives by allowing individuals to keep more of their income as they move into work, and by introducing a smoother and more transparent reduction of benefits when they increase their earnings. It will reduce the number of benefits and the number of agencies that people have to interact with as they move into work. This will make it easier for customers to understand their entitlements and easier to administer the system, thus leaving less scope for fraud and error. The effects of the policy will be to reduce the number of workless households by always ensuring that work pays. This document explores the expected impact of Universal Credit and provides evidence to justify the policy.