Key Challenges and Opportunities in Cloud Computing and Implications on Service Requirements: Evidence from a Systematic Literature Review Based on the findings from a systematic literature review (SLR), this paper presents a ranking of the key challenges and opportunities for cloud computing services and derives key requirements of effective cloud services. Top challenges include security, quality of service (QoS), privacy and resource management and scalability, whereas top benefits include reduced computing costs, consistent QoS and service level agreements (SLA), increased organizational agility and improved scalability. This paper also presents a ranking of 12 cloud security domains based on this SLR. Implications for building effective cloud computing services that meet users’ requirements are discussed.