Citizen science has gained widespread currency as a tool for ecological research over the\ud past decade. However, in the discipline of urban ecology, the existing contributions and future\ud potential of citizen science engagement, specifically in terms of knowledge gain, have not yet\ud been comprehensively explored. Here, we present a systematic review of published work on\ud the urban ecology of birds and butterflies in relation to their use of citizen science data\ud between 2005 and 2014. We compared the number of studies that used citizen science data\ud to the number of studies that could potentially have employed data derived from citizen science. The take-up rates of citizen science data were 21% and 26% for birds and butterflies\ud respectively. Most studies that employed citizen science used volunteer-derived data as primary data, and adopted Collegial, Collaborative and Contributional engagement modes to\ud the exclusion of Contractual and Co-created arrangements. There was no evidence that citizen science studies investigated a different organismal scale (community vs. species) com-\ud pared to the urban ecology literature. For both taxa, citizen science contributions were lower\ud than expected compared to their representation in the urban ecology literature for studies on\ud species-environment relationships at landscape and micro-environment scales, as well as\ud behavioural ecology in general. Other research topics that could benefit from further citizen\ud science involvement include breeding studies and guild analyses for birds, and multi-taxa\ud studies for butterflies. Promising models of citizen science engagement for urban ecology are\ud highlighted in relation to their thematic foci and methodological detail, and a number of\ud research questions that could be productively addressed using citizen science are identified.\ud The dynamics of contemporary engagement between citizen science and urban ecology\ud described by this review could inform the design and refinement of urban ecology - citizen science programmes in order to optimise their scientific contributions.