<p>Microalgae, a diverse assemblage of oxygen-generating photosynthetic organisms, demonstrate autotrophic, mixotrophic, and heterotrophic metabolic modes, facilitating adaptive regulation of their activity under different culture conditions and providing extensive biotechnological potential. Recently, there has been a growing interest in the cultivation of microalgae as biofilms owing to their potential for efficient biomass generation in confined systems and a wide range of industrial applications. This review offers a comprehensive overview of microalgal biofilm development, emphasizing adhesion mechanisms, variations in biofilm structure across diverse substrates, and the impact of critical physical parameters including cell density, size, morphology, and surface charge. Furthermore, the review examines the incorporation of different methods to attain a comprehensive understanding of biofilm development and molecular behavior while preserving biofilm integrity. The discussion encompasses the present challenges and future prospects of microalgal biofilms as biosensor components, highlighting their applications in environmental monitoring, on-chip biosensing, and biohybrid devices. The intrinsic benefits of microalgae, such as their capacity for self-regeneration, metabolic adaptability, and compatibility with optical and electronic systems, establish them as plausible candidates for sustainable biotechnological progress. By integrating mechanistic understanding, experimental methodologies, and application-focused approaches, this review seeks to establish a comprehensive framework for the advancement of next-generation microalgal biofilm technologies.</p>