Background: Aedes aegypti transmitted diseases have gained significant attention in Colombia, especially with the introduction of Chikungunya and Zika in the Americas during 2014 and 2015, and the increasing spread of the dengue virus (DENV). Even though important progress has been made in the reduction of these illnesses, evidence-based scaled-up programmes for effective control are limited in many settings, restricting the possibility of using evidence to inform the utilisation and expansion of new tools, technologies, and approaches. In one of Colombia's most hyper-endemic DENV cities (Girardot), the scaling-up of a community-based intervention under a multisectoral approach (“Girardot Aedes-Free”) was carried out between 2015 and 2018, aiming to reduce Ae. aegypti density, as well as dengue incidence. This programme included the distribution of insecticide treated water covers. The aim of this thesis was to investigate the effectiveness of the “Girardot Aedes-Free” intervention, and to assess the critical elements for implementing the intervention at scale and developing an effective multisectoral approach to scale-up the intervention. Methods: To assess the effectiveness of the scaled-up intervention on dengue incidence, the number of dengue cases and associated factors were analysed from available data sets from the local Colombian disease surveillance system. Different statistical analyses were used (Propensity score matching, Arma, and Differences in Differences (Diff in Diff)). In addition, different Ae. aegypti indices were calculated from baseline and follow-up household and public premises entomological data sets of study logs. The impact of the intervention in reducing Ae. aegypti indices in household and public premises was analysed using Diff in Diff, difference of endpoints and logistic regression models for both households and public premises. A process evaluation using a mixed-method approach was conducted to analyse the process of scaling up and implementing the intervention, as well as the importance of multi/intersectoral collaboration approach in scaling-up the intervention. Secondary data from semi-structured interviews with key actors, study logs, policy documents, and other official documents such as guidelines, minutes, statutes, and decrees were analysed to offer insight into the intervention implementation and context. Results: The “Girardot Aedes-Free” intervention can be defined as a complex community-based intervention that comprises four components that interacted at different levels (household covering productive Ae. aegypti breeding sites with insecticide-treated covers (ITCo), school, community, and institutional actions). The intervention reached 6127 households and 5709 insecticide-treated water-holding container covers were installed. Thirteen months after the intervention was implemented, entomological indices decreased overall in both intervention and control areas but decreased further in intervention areas, with significant differences, except for container indices (CI) and pupa per person indices (PPI) which increased in control areas. The CI decreased in intervention areas after the intervention (from 12% to 6%) and this decrease was significant (diff – 0.06, 95% CI [- 0.08, -0.04]) but increased slightly in control areas after intervention (from 13% to 15%), although the differences were not significant (diff 0.02 95% CI [-0.02, 0.06]). The Breteau Index (BI) decreased from 22.6 to 11.7 in intervention areas (diff 0.11, 95% CI [0.08, 0.14]) and from 31.6 to 27 in control areas (diff 0.05, 95% CI [ 0.00, 0.10]). Entomological indices in public spaces were higher than indices in households and decreased overall in both intervention and control areas after the intervention was implemented. The results of logistic regression models for both households and public spaces showed that after the intervention, there was a lower likelihood of finding immature forms of Ae. aegypti in intervention areas compared to control areas. Regarding impact on the reduction of dengue cases, although there is some evidence in favour of the intervention, there is no conclusive evidence. The scaling-up of “Girardot Aedes-Free” complied partially with a “vertical approach” (conducted and taken up by the governmental sector) and a “horizontal approach” (replication of a successful intervention). Two main factors hindered the expansion of the intervention and its integration into vector control polices and hence the sustainability of the intervention. These included 1. territorial governance, such as management and leadership, technical capacity, participation and institutional structure of a territory, and complexity of installation of household level intervention components and 2. political will of the local authority (Mayor). Furthermore, it was evidenced that the multisectoral collaboration was established under a genuine collaboration and has the potential to be successful in time. However, the are some challenges, including lack of human and financial resource mobilization and allocation, lack of monitoring system of actions, that need to be addressed to maintain its impetus. Conclusion: The outcome evaluation indicates that the intervention can reduce dengue vector populations but there is no conclusive evidence that the intervention can reduce dengue incidence. Greater coverage of the intervention, improved vector and dengue surveillance systems and sustainability of the multisectoral approach (led by the Mayor of the municipality) are required for further impact. The understanding of the process of implementation of scaling-up a vector control intervention provided useful information on how to scale-up and how to build and implement a multisectoral approach for the control and prevention of dengue and what factors must be addressed. The information from this study will support recommendations to improve DENV and Ae. aegypti prevention and control in Colombia and other developing countries. Furthermore, the evaluation of the multisectoral approach as part of a vector control intervention will help strengthen other multisectoral collaborations that have been implemented in Colombia following national guidelines and yet are not sustainable or functioning.