Bluetongue virus (BTV) is a double-stranded RNA virus of the Orbivirus genus, transmitted by Culicoides midges and responsible for bluetongue, an economically important disease of ruminants. With a segmented genome, BTV can undergo reassortment when two strains infect the same cell, driving viral evolution and genetic diversity. Epizootic haemorrhagic disease virus (EHDV), another Orbivirus, shares vectors, hosts, and epidemiological patterns with BTV, making coinfections in the field possible. Superinfection exclusion (SIE), where a primary infection prevents secondary infection, has been observed during asynchronous BTV coinfection. However, the impact of different variables, other orbiviruses (e.g., EHDV), and the mechanisms of SIE remain unclear. While BTV reassortment is well documented, most studies focus on synchronous infections; the effects of asynchronous coinfection on reassortment are less understood. This thesis investigated the interactions between orbiviruses during coinfection to better understand orbivirus evolution and genetic diversity. Work presented highlighted the outcome of BTV coinfection was partially dependent upon infection order, strain combination, timing, cell line, and multiplicity of infection (MOI). SIE occurred under specific conditions, though not all strains were capable of excluding superinfection. Preliminary data suggest SIE is established early in infection. Genome segment reassortment occurred frequently in both synchronous and asynchronous coinfections, provided full exclusion did not occur. Partial exclusion reduced the extent of reassortment but led to higher genetic diversity within the superinfecting viral population compared to the initial virus. Following asynchronous coinfection, BTV excluded EHDV infection and EHDV excluded BTV infection. Overall, the work presented highlights the complexity of Orbivirus coinfections, SIE dynamics, and the drivers of BTV genetic diversity. These findings advance our understanding of Orbivirus evolution and may inform future surveillance and control strategies for BTV and related viruses.