The polycentric urban spatial structure has attracted extensive discussion from researchers and policymakers worldwide. Despite its recognition as a more representative contemporary urban spatial structure, research into polycentricity still confronts a set of challenges, including an ambiguous definition, a lack of empirical evidence supporting its promised benefits, and uncertainties in its description and implementation in planning policies and practice. This work seeks to clarify the definition and measures of polycentricity across multiple planning contexts and applies these measures to explore transitions in the urban structures of real-world cities. More importantly, this work aims to empirically substantiate the promised advantages or outcomes of polycentricity, particularly in achieving more efficient, balanced, and sustainable territorial development. Specifically, Chapter one embarks on a literature review to resolve or clarify the origins, concepts, measures, spatial scales, and theoretical underpinnings of polycentricity across different contexts and developmental scenarios. I then offer a theoretical framework for polycentricity, which guides the development of this dissertation and may serve as a research agenda for future research. Chapter two (the first paper) addresses the thorny question of how to measure polycentricity using spatial statistical methods and explores the spatiotemporal evolution of urban spatial patterns in Chinese regions over the last two decades. My work challenges the notion that Chinese regions are generally becoming more polycentric; instead, I find that a monocentric tendency is predominant among medium- and small-sized regions. For larger regions, regional policies, enclave development (e.g., economic zones, industrial parks) and agglomeration inefficiencies contribute to their greater degree of polycentricity. In Chapter three (the second paper), I empirically examine whether polycentricism can simultaneously achieve both economic growth and regional equity in German metropolitan regions. This is motivated by the European Union’s spatial policies that promote polycentrism to achieve multi-objective regional goals. The results reveal that a polycentric configuration mitigates regional disparities, as it allows peripherals to “borrow size” from nearby core cities. However, the economic performance of core cities is adversely affected as they share their growth with surrounding small cities, and polycentric regions do not perform better economically than their monocentric counterparts. I conclude that achieving economic growth and greater equity simultaneously is not a viable objective for polycentrism. In response to the increasing challenges posed by climate change, Chapter four (the third paper) analyzes whether certain urban spatial patterns can mitigate the urban heat island (UHI) effect in German metropolitan regions using multi-sourced remote sensing imagery and nonparametric regression, I find that a polycentric spatial pattern is advantageous in mitigating extremely high temperatures near CBDs in large and highly populous regions.