Hereditary retinal disease is a significant cause of visual loss throughout the world. The underlying causes are, however, extremely varied. One group of these disorders preferentially affects the photoreceptors that are essential for colour vision and vision in normal daylight. These are the cone and cone-rod dystrophies which form part of a heterogeneous group of retinal dystrophies. Compared to diseases such as retinitis pigmentosa, which preferentially affect the rod photoreceptors, this group of disorders has been relatively poorly studied. Molecular genetic studies to date have identified mutations in eight different genes causing cone dystrophy. Many more, however, remain to be discovered. A number of families with different classes of cone, cone-rod and macular dystrophy were studied at a molecular genetic level. Mutation screening of genes previously implicated in achromatopsia identified new mutations and revealed a subset of individuals for whom no mutations could be found and, thus, a basis for further study of the heterogeneity of this disease. This has led to the identification of a novel gene for achromatopsia. A similar approach for a group of patients with blue cone monochromacy indicated the genetic basis of disease in all individuals studied. Candidate gene analysis in a group of patients with an X-linked cone dystrophy associated with colour vision deficiency suggested a novel locus for this disease. Linkage analysis in three families with macular disease identified three novel linkages. Screening for mutations in a novel candidate gene in a family with a cone-rod dystrophy (CORD7) identified a putative disease-causing mutation that implicates a new pathway in retinal disease. This thesis extends the breadth of knowledge on the molecular basis of retinal diseases. This is important since the clinical management of a particular disorder will benefit from a precise knowledge of the gene mutation involved and with the development of disease therapy, this research will lay the foundation for utilising novel treatment strategies in the future.