To incorporate by reference is a practice where a document includes a mention of a second document, with language indicating that the second document should be considered part of the first. The second document is usually appended to the first for review, but rather than being treated as an addendum to the original document, it is read as though it is wholly integrated into the original document. People must use this practice with care, as there may be cases when it is not considered legally valid.
This practice dates to an era when legal documents were produced laboriously by hand or by typewriter. Reproducing text to include it in another document was a painstaking process and people would instead incorporate by reference, mentioning the other document and attaching a copy. In order to be considered valid, the attached document must be clearly discussed and described in the original, making it obvious that it is indeed intended to be incorporated.
The decision to incorporate by reference can save space and time in the process of drafting a legal document. These can be important concerns with some kinds of documents, where citing references inline with the text could be a laborious process. As long as the references are clear and the documents are attached appropriately, the practice is usually valid and is considered acceptable. Not all attorneys are familiar with the standards for legal documents and if there are questions about whether an incorporation by reference will be allowed, it is advisable to consult a legal expert to get advice.
Wills are the area where an incorporation by reference can become especially problematic. There is a concern that people could attach falsified documents to a will, expecting the clauses in those documents to be executed along with the original. If documents are appended after the page signed by witnesses, it would be possible for someone to add them after the will was witnessed in the hopes of passing them off as valid.
In a will, if people want to incorporate by reference, the will itself must make it clear that the attached documents are intended to be read as part of the will and the descriptions cannot be vague, as there must be no room for substitutions. In the case of a holograph, a handwritten and unwitnessed will, if the document is used as an attachment to a will, it must be the original, not a copy.