This six days helpdesk review provides an overview of academic, policy and practitioner literature that explores lessons or evidence from efforts to establish joint operating principles agreed by humanitarian actors to improve humanitarian access and factors that contributed to their success or failure. Given the diffuse nature of the evidence base, this report is structured in three parts. First part will provide an overview of access constraints faced by humanitarian actors and factors that may enable or constrain the delivery of humanitarian aid, and an overview of joint operating principles and lessons learned. Part 2 provides an annotated bibliography of global and country specific readings that touch on, or have relevance, for the development of joint operating principles and humanitarian access. Part 3 provides examples of operating principles. A key message that emerges from this report is that there is a clear need for more evidence and independent academic research to understand the tensions and strategies used to overcome restrictions to humanitarian access – indeed some of the tensions highlight contradictions in approaches between actors within the humanitarian community regarding negotiating access, establishing red lines and ultimately have an influence on the viability of joint operating principles. Finally, in order to develop functional and appropriate joint operating principles a number of priorities are identified from existing literature. First of all, there is a need to strengthen analytic capacity of humanitarian actors to address the increasingly complex and complicated of humanitarian issues. Secondly, it is imperative for humanitarian actors to focus on strengthening their collective leadership. Next, resetting the relationship with the belligerents needs to be drawn to reduce the indirect benefits the government (or others) is accruing from the humanitarian operation. Consequently, improving the capacity to manage risk by engaging those actors with insights based on historic experience of how to navigate complex contexts. Finally, there is a need to acknowledge the heterogeneity of humanitarian actors and the the significant role of national and local staff.