Software systems become progressively more complex and difficult to maintain. To facilitate maintenance tasks, project managers and developers often turn to the evolution history of the system to recover various kinds of useful information, such as anomalous phenomena and lost design decisions. An informative visualization of the evolution history can help cope with this complexity by highlighting conspicuous evolution events using strong visual cues. In this paper, we present a scalable visualization technique called evolution spectrographs (ESG). An evolution spectrograph portrays the evolution of a spectrum of components based on a particular property measurement. We describe several special-purpose spectrographs and discuss their use in understanding and supporting software evolution through the case studies of three large software systems (OpenSSH, KOffice and FreeBSD).