Recently, carbon and silicon research has seen an outburst of new structures, experimentally observed or theoretically predicted (e.g., small fullerenes, heterofullerenes, schwarzite, and clathrates) with attractive properties. This book reviews these exotic futuristic species and their potential applications and critically examines the predicting models and the possible routes for their synthesis. The book starts with a review of 2D and 3D crystals based on carbon and/or silicon. The second part of the book is devoted to the description at the nanoscale of the new structures and complex architectures that ensue from them. The originality of the book lies in the fact that it deals with these scarcely evoked structures. The book is, therefore, complementary to the wide existing literature dedicated to popular nanostructures such as graphene, nanotube, and fullerenes.