We present a novel theoretical model to explain recipients' psychological processes in street art experience (SAE). Our model addresses a critical gap in empirical aesthetics, as existing models primarily focus on museum or gallery ("white cube") settings, which assume focused and uninterrupted art engagement—an assumption that hardly applies in street settings. It operationalizes art engagement through five mechanisms: aesthetic attitude, aesthetic attention, deep processing, flow experience, and aesthetic evaluation. The model identifies three sources of instability—personal, artifactual, and environmental—that account for the varied nature of art engagement on the street compared to museums or galleries. Consequently, the model differentiates between an art mode, characterized by the complete presence of art engagement, and a life mode, characterized by the complete absence of art engagement. To accurately capture SAE realities, based on a three-way interaction among recipient readiness (personal), artwork quality (artifactual), and environmental pleasantness (environmental factors), the model theorizes eight SAE scenarios, encompassing the polar states (art mode and life mode) and six intermediate partial engagement states that remain underexplored in the literature. Drawing on these components, determinants and psychological outcomes of SAE are hypothesized for empirical testing in future research. This model impacts fields beyond psychology, including street art studies dominated by cultural and sociological approaches, as well as urban design concerned with urban environmental quality and its consequences for city dwellers' well-being and life quality.