The chapter discusses the organization and transformation of nanostructures across extended length scales, emphasizing the spontaneous chemical assembly and transformation of building blocks rather than physical methods. It highlights the interplay between aggregation and crystallization, which can lead to mesoscale self-assembly and cooperative transformation of hybrid inorganic-organic building blocks to produce complex nanostructures. The authors propose that similar mesoscale processes are relevant to models of matrix-mediated nucleation in biomineralization. The chapter covers kinetic control of nucleation and growth, aggregation-mediated crystal growth, mesoscale self-assembly of nanoparticle arrays, and mesoscale transformations leading to emergent nanostructures. It also explores the role of macromolecules and surfactants in influencing crystal textures and morphologies, as well as the formation of hierarchical and hybrid nanostructures through coupled inorganic and organic transformations.The chapter discusses the organization and transformation of nanostructures across extended length scales, emphasizing the spontaneous chemical assembly and transformation of building blocks rather than physical methods. It highlights the interplay between aggregation and crystallization, which can lead to mesoscale self-assembly and cooperative transformation of hybrid inorganic-organic building blocks to produce complex nanostructures. The authors propose that similar mesoscale processes are relevant to models of matrix-mediated nucleation in biomineralization. The chapter covers kinetic control of nucleation and growth, aggregation-mediated crystal growth, mesoscale self-assembly of nanoparticle arrays, and mesoscale transformations leading to emergent nanostructures. It also explores the role of macromolecules and surfactants in influencing crystal textures and morphologies, as well as the formation of hierarchical and hybrid nanostructures through coupled inorganic and organic transformations.