Microwave-assisted synthesis (MAS) has emerged as a powerful and versatile approach for the preparation of nanomaterials with controlled composition, morphology, and functional properties. By coupling electromagnetic energy directly into reactive media, MAS offers substantially accelerated reaction kinetics, reduced energy consumption, and novel pathways for phase formation that are often inaccessible or inefficient under conventional thermal processing. These attributes particularly render the MAS more attractive for the fabrication of nanomaterials targeted at energy conversion and storage (photocatalysts, electrocatalysts, batteries and supercapacitor electrodes) and for environmental technologies (adsorbents, photocatalysts for pollutant degradation, membranes, and remediation agents). However, the translation of MAS from laboratory demonstrations to robust, reproducible, and scalable manufacturing faces technical and conceptual challenges: the selection and control of microwave-specific parameters (frequency, power density, irradiation mode), reactor design (single-mode versus multimode, pressure- and stirring-capabilities), etc. The interplay between dielectric properties of reactants and solvents determine heating heterogeneities, localized hotspots and nonequilibrium phenomena that influence nucleation and growth. Moreover, The existence of genuine non-thermal microwave effects and their magnitudes remain contentious and require careful experimental design and in-situ diagnostics. This chapter provides a rigorous, parameter-focused account of MAS for nanomaterials, integrating electromagnetic and thermochemical principles with practical reactor considerations. It surveys synthesis modalities (microwave solvothermal/hydrothermal, microwave-assisted sol–gel and solid-state, microwave plasma and aerosol routes), delineates the principal advantages and limitations, and discusses strategies for scale-up, process control, and characterization. Throughout, emphasis is placed on examples and metrics pertinent to energy and environmental applications, and on life cycle and safety considerations that are essential for responsible deployment. The chapter concludes with a forward-looking perspective on research priorities to consolidate MAS as a reproducible, sustainable, and industrially relevant route to functional nanomaterials.