Simple sequence repeats (SSR) are extensively used as genetic markers for studies of diversity, genetic mapping, and cultivar discrimination. The informativeness of a given SSR locus or a loci group depends on the number of alleles, their frequency distribution, as well as the kind of application. Here I describe several methods for calculating marker informativeness, all of them suitable for SSR polymorphisms, proposed by several authors and synthesized in an Information Theory framework. Additionally, free access software resources are described as well as their application through worked examples.