When synthetic polymers are produced, the molecular architecture properties such as chain length, composition. block length, branch length, branch location, etc. are distributions. Similarly, the polymer morphology and physical form resulting from a polymerization step are also distributions. These include crystal size, particle size, microdomain sizes, etc. The end use properties of the polymer product are greatly influenced by the distributions resulting from polymerization. The particular type of distribution and it's moments depend on the kinetic mechanism, the type of reactor employed, and the number of phases involved. This talk will review the types of distributions that arise, and discuss how the reaction engineer can influence the type of distribution and the moments of the distribution through choice of kinetic mechanism, reactor, and operating conditions .