The effects of urbanisation, high population growth rate and increase in impervious surfaces has significantly changed urban climatic regimes leading to the escalation of the Urban Heat Island (UHI) phenomenon. This is a phenomenon that has occurred due to high temperatures in the air and surface of the cities compared to their rural environment and has become one of the major environmental issues of 21st century. It does not only increase the effects of global climate change, but also affects the livability of population in urban areas, their health, and energy consumption. The content of the study on UHI is however not well integrated because the research has grown at a high rate in the last twenty years and it has been divided into various fields; some of these include climatology and urban design, remote sensing, and environmental planning. As such, the UHI research is highly complex in terms of evolution, structure, and knowledge areas, thus necessitating a thorough investigation of the area so as to inform future research and policy. The proposed study aims to systematically review and map the current literature on Urban Heat Island in the world and uses the tools of bibliometric and science mapping. The goals specific to the research are as follows: (1) to trace the temporal dynamics of publications on UHI between 1999 and 2025; (2) to establish the most impactful authors, institutions, countries, and journals active in this area; (3) to examine how keywords are co-occurring and identify the key thematic groups; and (4) generalise on the key environmental and spatial factors which are influencing the intensity of UHI as evidenced in the body of published research. Through a combination of quantitative bibliometric measures and qualitative content analysis, this study will fill the gap between descriptive mapping of science and interpretive synthesis by providing an evidence based framework of the direction of UHI research. On 17 May 2025, a systematic literature search was carried out in the Web of Science Core Collection database. The search resulted in 604 documents, 58 of which were journal articles, 13 conference papers, 6 reviews, and the last 48 documents were published between 1999 and 2025. The inclusion criteria were: publications that were in English; studies that clearly stated UHI processes, causes, mitigation, or modelling; that bibliometric metadata (authors, affiliations, keywords, citations) was available. The data were analysed with VOSviewer, which pays attention to three dimensions, i.e. co-authorship networks (authors, countries, institutions), co-citation analysis (after identifying intellectual foundations) and key words co-occurrence analysis (after identifying research frontiers and clusters). The bibliometric search was complemented with the qualitative systematic review of the selected high-citation sources to find major indicators of UHI level, which are vegetation cover, impervious surface ratio, albedo, building density and land-use configuration. The UHI-related publications have shown a consistent rising trend since 1999 to 2025 with a sharp increase since 2018, as more and more people globally are becoming aware of the problem of city and climate, and high-resolution remote sensing data are available. China, the United States and Australia became the most fruitful ones, as they contributed more than 50 per cent of all publications. Chinese Academy of Sciences, Nanjing University and Arizona State University were the most active institutions. There was a very good cooperation between the Chinese and the U.S. researchers and this was a pointer to a mature and interconnected research network.  Oke, Weng and Zhou are the most frequently mentioned authors who developed theoretical and methodological premises in UHI studies. The popular publication outlets like Urban Climate, Remote Sensing of Environment and Building and Environment are the most popular journals, and the fact that the discipline is interdisciplinary. Co-occurrence analysis revealed that there are four key thematic clusters that define the intellectual structure of the UHI research: (1) urban climate and public health; (2) thermal remote sensing and surface temperature analysis; (3) urban form and design strategies; and (4) mitigation and adaptation strategies. A review of the literature found 23 indicators of environment and space with impacts on the intensity of UHI. The most commonly reported ones were vegetation cover (NDVI), impervious surface ratio, surface albedo and sky view factor. The findings support the claim of vegetation and reflective-covered areas significantly alleviating the effects of heat accumulation, and dense urban territories and dark substances contribute to UHI. The results indicate that the UHI research of the world has been transformed by descriptive case studies to integrative, data-focused, and mitigation-based models. The increased use of remote sensing methods, machine-learning, and highly-resolved climate models has made possible more accurate measurements of the thermal phenomena in the urban environment. Nevertheless, there is still a geographical prejudice, and most of these studies are based in East Asia, North America, and Western Europe whereas quickly growing urbanising areas in the Global South, specifically the Middle East and Africa, are still underrepresented. Methodologically, there remains little integration of the urban morphology indicators and micro-climatic simulations. Future research must follow multi-scale methodology that will integrate local field experiments and global data sets in order to increase the possibility of generalizing findings. Furthermore, urban planners, climatologists, and other specialists in the field of public health should collaborate interdisciplinarily in order to create urban environments which would be climate resilient. The systematic review and bibliometric analysis is a holistic description of 25 years of UHI research. The paper provides a map of the intellectual field in the world, determines the flows of research, and generalises the forces of the environment that influence urban thermal processes. The findings highlight the primary importance of the green infrastructure, surface albedo control and optimal urban form in reducing heat buildup and enhancing urban resilience. The study becomes part of the theoretical view of UHI by providing both quantitative and qualitative information to help the evidence-based policy and planning interventions towards sustainable urban development.