Polyploids are organisms with multiple sets of chromosomes in excess of the diploid number (Acquaah, 2007; Chen, 2010; Comai, 2005; Ramsey and Schemske, 1998). Polyploidy is common in nature and provides a major mechanism for adaptation and speciation. Approximately 50-70% of angiosperms, which include many crop plants, have undergone polyploidy during their evolutionary process (Chen et al., 2007). Flowering plants form polyploids at a significantly high frequency of 1 in every 100,000 plants (Comai, 2005). Many studies have been carried out to understand the nature of polyploidism. This chapter seeks to illuminate some of these studies and explain the applications and implications of polyploidy in plant breeding and other commercial ventures. To understand polyploidy, a few basic notations need be defined. The basic complete set of chromosomes is designated by āxā while the total number of chromosomes in a somatic cell is designated ā2nā. The total number of chromosomes in a somatic cell is twice the haploid number (n) in the gametes (Acquaah, 2007; Otto and Whitton, 2000). The ploidy of some of the major crops in the world is represented in Table 5.1.