Ph.D. / South Africa has the highest biodiversity of tortoises in the world with possibly an equivalent diversity of apicomplexan haematozoans, which to date have not been adequately researched. Prior to this study, five apicomplexans had been recorded infecting southern African tortoises, including two haemogregarines, Haemogregarina fitzsimonsi and Haemogregarina parvula, and three haemoproteids, Haemoproteus testudinalis, Haemoproteus balazuci and Haemoproteus sp. A. The taxonomy of all of these species was questionable, and therefore one goal of this study was to examine at least some in great detail with the view to resolving taxonomic issues. This involved using a number of techniques such as light microscopy and image analysis, transmission electron microscopy, and molecular analysis. Outcomes were the transfer of one Haemogregarina species (Haemogregarina fitzsimonsi) to the genus Hepatozoon, the suggestion that the genus Hemolivia might be more appropriate for another haemogregarine (Haemogregarina parvula), the synonymisation of two known species of Haemoproteus (Haemoproteus balazuci with Haemoproteus testudinalis), and the naming of a third haemoproteid (Haemoproteus natalensis Cook, Smit and Davies, 2010). In addition, a likely new species of haemogregarine (Haemogregarina sp. A.) was described. To achieve all this, 367 tortoises were collected representing 62% of the species and all five genera, of South African tortoises. Tortoises were both wild (287) and captive (80), with these being both live (270) and dead (97) when taken. They were located in four different provinces, including Gauteng, KwaZulu-Natal, the Northern and the Western Cape, and in four different biomes (semi-arid grassland, Kalahari desert, subtropical thorn bushveld, and coastal endemic fynbos). Light photomicroscopy examination of Giemsa stained peripheral blood smears prepared from the subcarapacial vessels of live tortoises allowed for descriptions and comparisons of the observed haematozoans. Of the live tortoises, 14.8% had haemogregarines, including 13.3% with H. fitzsimonsi, 0.7% with H. parvula, and 0.7% with a previously unknown, intraleucocytic, Haemogregarina sp. A. A further 1.1% had haemoproteids, including 0.7% with Hp. testudinalis/Hp. balazuci and 0.4% with Haemoproteus sp. A. The host and locality records of previously described haematozoan species were increased and records for likely new species provided. Subtropical areas (KwaZulu-Natal) compared to arid regions (Northern Cape) presented with a higher diversity of apicomplexans, along with a higher prevalence of ticks, possible vectors of the tortoise blood parasites. Overall, male tortoises had the highest haematozoan and tick prevalences compared to females and juveniles,