Microsatellite loci are important for genetic studies due to the many desirable qualities they possess. However, speculation continues about the types of mutation that act on microsatellites. In particular, whether different motif types for stable, non-coding loci have different rates of mutation is not clear. This thesis addresses three aspects of the mutation problem. First, an investigation of the types of mutation acting on microsatellites is presented. The models compared are the single-step stepwise mutation model and the infinite alleles model. Second, two models of allele size distributions under a non-symmetric, single-step SMM model are proposed. Third, an indirect estimate of mutation rates for di- and tetranucleotide loci is obtained.