This paper reports on the design and implementation of Chianti, a change impact analysis tool for Java that is implemented in the context of the Eclipse environment. Chianti analyzes two versions of an application and decomposes their difference into a set of atomic changes. Change impact is reported in terms of affected tests whose execution behavior may have been modified by the applied changes. For each affected test, Chianti also determines a set of affecting changes that were responsible for the test’s modified behavior. We evaluated Chianti on 6 months of data from M. Ernst’s Daikon system, and found that, on average, 62.4% of the tests is affected. Furthermore, each affected test, on average, is affected by only 5.6% of the atomic changes. These findings suggest that change impact analysis is a promising technique for assisting developers with program understanding and debugging.