The snapshot package helps the owner of a LaTeX document obtain a list of the external dependencies of the document, in a form that can be embedded at the top of the document. It provides a snapshot of the current processing context of the document, insofar as it can be determined from inside LaTeX. If a document contains such a dependency list, then it becomes possible to arrange that the document be processed always with the same versions of everything, in order to ensure the same output. This could be useful for someone wanting to keep a LaTeX document on hand and consistently reproduce an identical DVI file from it, on the fly; or for someone wanting to shield a document during the final stages of its production cycle from unexpected side effects of routine upgrades to the TeX system.