Backup or preservation of websites is often not considered until after a catastrophic event has occurred. In the face of complete website loss, webmasters or concerned third parties have attempted to

recover some of their websites from the Internet Archive. Still others have sought to retrieve missing

resources from the caches of commercial search engines. Inspired by these post hoc reconstruction

attempts, this dissertation introduces the concept of lazy preservation– digital preservation performed as a result of the normal operations of the Web Infrastructure (web archives, search engines

and caches). First, the Web Infrastructure (WI) is characterized by its preservation capacity and

behavior. Methods for reconstructing websites from the WI are then investigated, and a new type

of crawler is introduced: the web-repository crawler. Several experiments are used to measure and

evaluate the effectiveness of lazy preservation for a variety of websites, and various web-repository

crawler strategies are introduced and evaluated. The implementation of the web-repository crawler

Warrick is presented, and real usage data from the public is analyzed. Finally, a novel technique for

recovering the generative functionality (i.e., CGI programs, databases, etc.) of websites is presented,

and its effectiveness is demonstrated by recovering an entire Eprints digital library from the WI.