That which is required or compulsory. Containing a command; preceptive; imperative; peremptory. A provision in a statute is mandatory when disobedience to it will make the act done under the statute absolutely void; if the provision is such that disregard of it will constitute an irregularity, but one not necessarily fatal, it Is said to be directory. So, the mandatory part of a writ is that which commands the person to do the act specified. Mandatory injunction. See Injunction.