[Truncated abstract] Grevillea and Leucadendron belong to Proteaceae and both have economic importance to the floriculture industry. Grevillea is a highly diverse genus endemic to Australia and very attractive for landscaping. Leucadendron is a South African Proteaceae but is cultivated in Australia and is well known as a cut flower. This thesis focuses on the application of DNA-based molecular markers to these genera. Several groupings within Grevillea were suggested by previous researchers based on morphological characteristics. In this thesis the monophyly of the groupings among 12 Grevillea species from New South Wales was tested using random amplified polymorphic DNA (RAPD) and inter simple sequence repeat (ISSR) analyses. To test the robustness of the data, UPGMA using Jaccard similarity, Neighbor Joining using total character difference and Wagner parsimony analyses were undertaken. The relationship trees generated supported monophyly of the groupings. Chloroplast DNA (cpDNA) was used to develop phylogenetic relationships among Leucadendron species. Inheritance and variation of cpDNA were evaluated using PCR-RFLP. The study demonstrated that cpDNA was inherited maternally and a phylogenetic tree of Leucadendron species using parsimony analysis was constructed. ... A fingerprinting study conducted using ISSR, produced a dendrogram showing the relationships among 30 cultivars. From the results, i a fingerprinting key was developed. Three examples of synonymous cultivar pairs were identified. In Leucadendron the male and female flowers develop on separate plants, and sex identification is only possible at time of flowering. ISSR, suppression subtractive hybridisation (SSH), and SSH combined with mirror orientation selection (MOS) were used in attempts of identifying sex-dependent DNA fragments at earlier stages of plant development. Neither of these techniques was able to identify sex-specific markers in Leucadendron. Nevertheless, the results did indicate that cpDNA copy number may differentiate male and female plants. Also, it was demonstrated that the genomes of male and female plants are quite homologous, which increases the difficulty in identifying sex-specific sequences. This thesis highlights the potential of DNA-based markers to determine species relationships in Grevillea and Leucadendron, as well as to identify Leucadendron cultivars. The information produced during the research for this thesis provides a basis for Grevillea and Leucadendron variety development and may be used to assist the design of interspecific crosses, to identify cultivars and the parents of hybrids. In addition, the results offer insights into the likelihood, problems and strategies of finding sex-specific markers for genes controlling sex in Leucadendron. ii