There is increasing emphasis on enhancing vegetation complexity in urban landscapes to deliver both ecological and social benefits, including improved human wellbeing, nature connectedness, and biodiversity support. Vegetation complexity achieved through combinations of trees, shrubs and grasses can be introduced in both urban greenspaces and streetscapes. While it is often assumed that such complexity improves urban microclimates and human thermal comfort, these effects are highly context-dependent, shaped by background climate, urban morphology, vegetation spatial structure, and plant traits. To investigate these dynamics, this chapter integrates a critical review of the literature with empirical data from three case study cities representing contrasting climate zones: Melbourne and Munich (temperate) and Hong Kong (humid subtropical). Using comparable methods, we assess the influence of multi-layered vegetation on human thermal comfort through in-situ microclimate measurements, applying standardized indices such as physiological equivalent temperature (PET) and universal thermal climate index (UTCI). Positive impacts are generally driven by enhanced shading and evapotranspiration, while potential drawbacks—such as reduced wind flow, increased humidity, and hindered pollutant dispersion may moderate benefits, especially in dense urban settings. Our empirical findings show that multi-layered vegetation consistently reduces thermal stress in greenspaces. In streetscapes; however, the outcomes are more variable due to constrained airflow, vegetation configuration, and local built form. At the same time, literature review findings using modeled output often diverged from empirical findings, emphasizing the need for context-specific calibration and ecological understanding. This study supports a shift toward integrated design thinking, where vegetation complexity is purposefully calibrated to balance thermal comfort, biodiversity, and urban function. Future cooling strategies must consider not only vegetation presence but also its growth-form combinations and interaction with built environments. To inform this, long-term, field-based studies on fully complex vegetation structures are needed to capture diurnal and seasonal variability in diverse urban contexts.