Records of a regularly conducted activity are admissible despite being hearsay, which is what makes documentary proof possible.

The foundation. The record was made at or near the time by, or from information transmitted by, someone with knowledge; it was kept in the course of a regularly conducted activity; making it was a regular practice; and the foundation is shown by a custodian or other qualified witness, or by certification.

Certification avoids live testimony. Written notice to the other parties and an opportunity to inspect are required, and the deadlines are short.

Trustworthiness. The opponent may still exclude the record by showing that the source of information or the circumstances indicate a lack of trustworthiness — the usual argument being that the record was prepared in anticipation of litigation rather than in the ordinary course.

Records of another business received and relied on are frequently admissible where the receiving business integrated them into its own records and relied on their accuracy. That saves a great deal of subpoena practice.

Absence of a record is admissible to prove an event did not occur, on the same foundation.

Practical planning. Identify the custodian for every category of document early. A key exhibit with no sponsor is discovered at the worst moment.