Although phase data can take on any value, it is generally only possible to measure phase as a principle value, i.e., wrapped within the range (-pi,pi]. Determining the unwrapped phase from its principle value is a topic of considerable interest in magnetic resonance imaging (MRI), as well as many non-medical disciplines. Despite their importance in image analysis, filters for manipulating phase information have not been incorporated into ITK. This article introduces the ITKPhase module, containing filters useful for understanding, analyzing, and unwrapping n-dimensional phase data, and also serves as a practical introduction to phase unwrapping.