Product engineering problems are considered that arise in the use of batch crystallization processes. Specifically forward and reverse process functions are identified that in the forward direction enable the calculation of product crystal size distributions (CSDs) from specified operating conditions, and in particular a specified temperature-time (T-t) profile. In the reverse direction the process function calculates the required processing conditions-the T-t profile-needed to make a specified product CSD. A series of example calculations is reported, based on the kinetics of the pentaerythritol-water system, that show that in the presence of nucleation and growth only, the relationship between desired, or target, CSD and required T-t profile is, in practice, unique. It is observed that some such profiles are either impractical or impossible, from which it is possible to conclude that the corresponding target CSD is itself impossible. A further example is considered in which the property function relating the product property (CSD) to the end-use properties (cake porosity and filtration time) enables the specification of a target CSD and of the process conditions necessary for its production. (c) 2006 American Institute of Chemical Engineers.