The W3C Provenance Working Group has published a Last Call Working Draft of Constraints of the Provenance Data Model. This document defines a subset of PROV instances called valid PROV instances. The intent of validation is ensure that a PROV instance represents a history of objects and their interactions which is consistent, and thus safe to use for the purpose of logical reasoning and other kinds of analysis. Valid PROV instances satisfy certain definitions, inferences, and constraints. These definitions, inferences, and constraints provide a measure of consistency checking for provenance and reasoning over provenance. They can also be used to normalize PROV instances to forms that can easily be compared in order to determine whether two PROV instances are equivalent. Validity and equivalence are also defined for PROV bundles and documents. Comments are welcome through 10 October.