Due diligence in a broad sense refers to the level of judgement, care, prudence, determination, and activity that a person would reasonably be expected to do under particular circumstances.

Due diligence in civil procedure is the idea that reasonable investigation is necessary before certain kinds of relief are requested.

For example, duly diligent efforts to locate and/or serve a party with civil process is frequently a requirement for a party seeking to use means other than personal service to obtain jurisdiction over a party. Similarly, in areas of the law such as bankruptcy, an attorney representing someone filing a bankruptcy petition must engage in due diligence to determine that the representations made in the bankruptcy petition are factually accurate. Due diligence is also generally prerequesite to a request for relief in states where civil litigants are permitted to conduct pre-litigation discovery of facts necessary to determine whether or not a party has a factual basis for a cause of action.

In civil actions seeking a foreclosure or seizure of property, a party requesting this relief is frequently required to engage in due diligence to determine who may claim an interest in the property by reviewing public records concerning the property and sometimes by a physical inspection of the property that would reveal a possible interest in the property of a tenant or other person.
Due diligence is also a concept found in the civil litigation concept of a statute of limitations.

Frequently, a statute of limitations begins to run against a plaintiff when that plaintiff knew or should have known had that plaintiff investigated the matter with due diligence that the plaintiff had a claim against a defendant. In this context, the term "due diligence" determines the scope of a party's constructive knowledge, upon receiving notice of facts sufficient to constitute "inquiry notice" that alerts a would-be plaintiff that further investigation might reveal a cause of action.