Globally over 2.8 million children aged between 0-18 years were living with HIV in 2019. ART substantially reduces mortality but the pre-requisite step for accessing treatment is HIV diagnosis. Coverage of HIV treatment in children has lagged behind when compared to adults largely because of delayed diagnosis. Children experience unique challenges to access HIV testing. Existing strategies for paediatric HIV testing, which largely are similar to those used for adults, have not been effective in addressing the HIV diagnosis gap in children. Index-linked HIV testing (HIV testing offered to household members and sexual contacts of individuals living with HIV) for children and adolescents may improve HIV testing uptake and have high HIV yield. Offering index-linked HIV testing for children and adolescents in both facility and community settings may be an effective strategy to help bridge the HIV testing gap. The aim of this research was to evaluate facility and community-based approaches for index-linked HIV testing for children and adolescents aged 2-18 years in Zimbabwe. This PhD combined mixed methods research in the city of Bulawayo and in Matabeleland South province between January 2018 and May 2019. Overall, 2870 index patients had 6062 children who were eligible for HIV testing in their households. Indexes were offered a choice of facility-based or community-based HIV testing (either home-based HIV testing by a health provider or an oral mucosal transudate (OMT) HIV test kit given to a caregiver to test their child(ren)). HIV testing was accepted for 5326 (87.9%) children, and 3638 children were tested (60.0% HIV testing uptake). The HIV prevalence and yield were 1.1% and 0.6% respectively. Older children and adolescents were less likely to be tested when compared to children aged 2-5 years. Children had increased odds of being tested if community-based HIV testing was chosen over facility based HIV testing. There was inadequate emphasis on paediatric HIV in routine HIV care which had a negative impact on subsequent uptake of HIV testing for children. Once the decision to test had been made, access to facilities was sometimes challenging and alleviated by community-based HIV testing. OMT tests, although previously validated for HIV testing in adults and widely used in HIVST for adults had not been validated for HIV testing in children <12 years. In this research, OMT sensitivity was 100% [97.5% CI: 94.9% to 100%]) and specificity was 99.9% [95% CI: 99.6% to 100.0%] among children aged 2-18 years when compared to national HIV testing algorithms. A further application of OMT testing evaluated as part of this research was caregiver’s ability to test their children for HIV and interpret test results. Overall, most caregivers correctly collected oral fluid (87.1% without provider demonstrations and 96.8% with demonstrations from a provider, p=0.002). The HIV yield was low when compared with blanket HIV testing approaches in similar settings. There is a need to improve messaging on the importance of HIV testing for children and adolescents and to provide support to caregivers and their families in order to increase HIV testing uptake. Addressing access barriers through the provision of community-based HIV testing can optimise index-linked HIV testing. Caregiver-provided testing using OMTs is a feasible and accurate HIV testing strategy for children and can also be used to improve uptake of HIV testing for children.